Adding fastpath and name parameters to docstring for Series class and others. 
- [x] closes #27178
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

I modified the docstring for the Series class to include the "fastpath" and "name" parameters.  I searched the code base, and also modified the docstrings for the following classes in a similar way:

Categorial
CategoricalIndex
Grouping
Index
MultiIndex
PeriodIndex
RangeIndex

It appears that fastpath is definitely used internally, and is not deprecated.  There were no other examples of fastpath being documented in the parameters section of a docstring, so I went with this convention:

fastpath : bool, default False
        Internal use only
Thanks for the PR! I'm not sure about documenting this more. The note is pretty clear that it's *internal only* I think this generates more questions than it solves.

Would the alternate just to be to remove it from all documentation? Will, happy to help!

I thought about removing it entirely, as that would probably be the clearest message to the user.  However, it looks like Sphinx is using autosummary to build the first part of the documentation and is querying the class' __init__ method to do so.  So as long as fastpath is a valid parameter to the constructor, it will show in the documentation.  

I'm new to Sphinx so I'm not sure if there is an easy way to override this behavior to hide certain parameters.  So I think our options are:

1. Do as I have done in the pull request to at least let users know to leave the fastpath parameter alone.

2. Do some Sphinx wizardry so that it ignores the fastpath parameter when building the doc. 

3. Eliminate the fastpath methodology from the code base.

I think I understand why the fastpath functionality was originally used internally.  There are way more sanity checks and exception handlers used when fastpath=False.  fastpath=True assumes that the caller has done their homework and isn't passing in garbage.  Makes sense for an internally used function.  

I'm open to any of the three options,  what do you think? I _think_ I've identified the only place where Series fastpath is used and plan to get rid of it. I only found one use of it for Series in this block of code in pandas/core/frame.py

```python
    def _box_col_values(self, values, items):
        """
        Provide boxed values for a column.
        """
        klass = self._constructor_sliced
        return klass(values, index=self.index, name=items, fastpath=True)
``` It sounds like the direction is to purge fastpath from the code base.  I'm going to go ahead and close this request in lieu of future pull requests that propose code changes to remove fastpath from classes other than Series.   As long as `fastpath` is not removed (and I don't see any immediate motion on that), it's better to document it as "Internal use only" than having people wonder what this is for and maybe even use it.

So I think this is still a valuable addition.