DOC: pd.read_csv doc-string clarification #11555
closes #11555 
Updated IO Tools documentation for read_csv() and read_table() to be consistent with the doc-string.

what exactly changed here?
 can you verify that these are in numpy-doc format, see [here](https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt)

mostly it comes down to a parameter like:

```
parm : datatype, optional/required, default value
     description
```
 ```
Parameters

Description of the function arguments, keywords and their respective types.

Parameters
----------
x : type
    Description of parameter `x`.
Enclose variables in single backticks. The colon must be preceded by a space, or omitted if the type is absent.

For the parameter types, be as precise as possible. Below are a few examples of parameters and their types.

Parameters
----------
filename : str
copy : bool
dtype : data-type
iterable : iterable object
shape : int or tuple of int
files : list of str
If it is not necessary to specify a keyword argument, use optional:

x : int, optional
Optional keyword parameters have default values, which are displayed as part of the function signature. They can also be detailed in the description:

Description of parameter `x` (the default is -1, which implies summation
over all axes).
When a parameter can only assume one of a fixed set of values, those values can be listed in braces, with the default appearing first:

order : {'C', 'F', 'A'}
    Description of `order`.
When two or more input parameters have exactly the same type, shape and description, they can be combined:

x1, x2 : array_like
    Input arrays, description of `x1`, `x2`.
```
 In terms of what was changed: I updated the IO Tools description of `read_csv()` that appears [here](http://pandas.pydata.org/pandas-docs/stable/io.html#csv-text-files) to match the doc string. I thought that's what the bug was getting at. I also slightly changed the wording describing the default behavior of the `header=` option.

I can go through and make any changes to put the doc string in numpy format, would you prefer that as a separate PR and/or should I drop the IO Tools doc changes?
 @frankcleary thanks. can you enumerate what changed (here), though. just for my edification.

yes, would like to conform to numpy-doc in this PR.
 Makes sense, I'll do that and update this PR later this week.
 @jreback The list is in io.rst, not in the docstring. So I think it does not need to follow the numpy-doc format?
 @jorisvandenbossche hmm, good point. I am not sure _what_ we actually do as we don't have too many places where we go thru the args of functions. is there a consistent pattern now (anywhere)? any reason _not_ to use a doc-string format? 
 The only other place I could find in the docs with a similar list of args is for `concat` in [merging.rst](http://pandas.pydata.org/pandas-docs/stable/merging.html#concatenating-objects). This also appears to have lagged behind the [`concat` docstring](http://pandas.pydata.org/pandas-docs/stable/generated/pandas.concat.html) in terms of updates (for example there's no  `copy=...`). I wonder if it's better to remove these lists from the *.rst documentation in favor of links to the docs generated from the docstrings themselves?
 @frankcleary the ideal thing would be to render the doc-strings in-line. as the out-of-syncness is annoying. Though if you simply want to fix it we can make that another issue.
 Looks like sphinx can do that, updated. Here's a sample of what the result looks like in the io docs:

![screen shot 2015-12-13 at 9 39 32 pm](https://cloud.githubusercontent.com/assets/5619798/11773688/0c65c1fc-a1e2-11e5-95fe-1ca9571e9dfb.png)
 @jorisvandenbossche how's this look to you
 Hmm, personally, if it looks exactly the same as the generated API page, I would just link to it rather than including it. 
But I also understand that keeping a separate list of the parameters up to date is more work, but I think it is nicer for the tutorial docs (so as one of the original commits in this PR: keep it as a list, but update the explanations).
 so after seeing this, I think I agree with @jorisvandenbossche 

let's revert back to just an updated list (and hopefully we can keep this updated).

@frankcleary can you update.
 Sure, I'll get to it this week.
 @frankcleary looks good. couple of points. 

I would like to have the options in the same order as `io.rst` sections. grouping if possible (e.g. the NA values together). I think this will be more logical.

All that said the more important options should be closer to the front if at all possible (I think that is how we had it). e.g. things like `index_col`, `header`, `sep`. 

So ok to reorg a bit (see if you can keep the code in sync as well). everything is passed by kw so that should be fine. Add a note in the whatsnew to say that the ordering of args was changed (in API section) as well.
 Makes sense, thanks. I will incorporate all those suggestions next weekend and post an update by Monday Jan. 18.
 Here's the order I'm thinking of in terms of logically organizing the arguments, along with the general idea behind the grouping I put them in. Any thoughts?

##### Basic

filepath_or_buffer
sep
delimiter

##### Column and index names and location

header
names
index_col
usecols
squeeze
prefix
mangle_dupe_cols

##### General parsing details

dtype
engine
converters
true_values
false_values
skipinitialspace
skiprows
skipfooter
nrows

##### NA handling

na_values
keep_default_na
na_filter
verbose
skip_blank_lines

##### Date handling

parse_dates
infer_datetime_format
keep_date_col
date_parser
dayfirst
thousands
decimal

##### Iteration

iterator
chunksize

##### Quoting and file format

compression
lineterminator
quotechar
quoting
escapechar
comment
encoding
dialect
tupleize_cols

##### Errors

error_bad_lines
warn_bad_lines
 @frankcleary a reorg like that would great!

(note you can prob use the `^^^^` to make these sub-sections in the docs (I think) so that they show up on the menu bar as groupings.
 I've got an update almost ready with the reorg and other suggested changes, but need to fix merge conflicts in the parsers.py docstring so I won't be able to finish it tonight. I will get it done this weekend.

Is this about what you're thinking in regard to the sections:

<img width="787" alt="screen shot 2016-02-03 at 10 53 41 pm" src="https://cloud.githubusercontent.com/assets/5619798/12808069/26ff52ac-cac9-11e5-9bdc-f86ef78f244e.png">
 Thanks for this!

One consideration:
- I think we should try to make the actual option name stand out a bit more (not it is a bit lost in the dense bullet point). Maybe using something like http://docutils.sourceforge.net/docs/user/rst/quickref.html#definition-lists ? (just an idea, would have to try out to see how it looks)
 Sorry, I was trying to push a clean history and it looks things are finished for this PR (can't reopen on a closed PR with a force pushed branch). I opened a new one here: https://github.com/pydata/pandas/pull/12256
