ENH: read-html fixes
Some updates and bug fixes. See release notes for more details.
- ~~`vbench` stuff~~ sort of pointless right now since we don't really have control over the speed of the parsing library
- ~~Figure out why `lxml` chooses to ignore things~~ reported a bug w/ example to lxml people
- ~~Figure out why `bs4`'s `thead.find_all(['th', 'td'])` parses differently than `lxml`'s `thead.xpath('.//thead//th|.//thead//td')` even when `lxml` is the `bs4` backend.~~ same as above

let me know when you need merging on any PR's
 this closes #3606, right?
 yep, that is fixed already. i might be able to get to the rest of this today, i know the 0.11.1 rls is due today...the annoyances of the parsing may have to wait tho or i might just open up the flavor argument to allow one of `'lxml', 'bs4', 'html5lib'` since `html5lib` is a bit more WYSIWIG than the others even if it's drastically slower.
 the main issue is the import errors.....
 that is also fixed in this.
 u r talking about #3605/#3607 right?
 yep...
 take your time...btw
 ok thanks. i'm working on a cmdline interface to store neurophys data and it's due tmrw so pandas may have to wait...
 @jreback @y-p what do u think about removing the _pure_ `lxml` option (then options would then be `lxml` and `html5lib` which correspond to the backend of `bs4` to use)? i think i was a little gung-ho about `lxml` being fast, but in reality the best is `bs4` + `html5lib`. Even though it's very slow, it gives correct output where `lxml` does not.
 @cpcloud I would rather see correct and slow then wrong but fast!

let's see **premature optimization is evil**

Can always add it back in 0.12 (or after) if you discover how to fix it. And you have the flavor option, so sort of 'easy' to add it. (course have to edit stuff to take it out...docs,install docs,docstrings...)

of course if there are cases where lxml can do better (and is correct), but bombs on other cases, then you could always raise on those (but that may be more trouble than its worth)
 i think the xpath implementation of lxml might be broken... :( 

@jreback can i leave the code for `lxml`/`bs4` + `lxml` in `html.py`? i would just make only `html5lib` available until i either figure out the issue or decide that it's not worth it...
 ok 
 @jreback this ready 2 go as soon as travis passes.
 that is odd. travis is not running arg
 ah there we go
 @cpcloud thanks...this is great...

I edited the v0.11.1 a bit (as this is new, just announcing it). I think an example is warranted. Maybe take a df, `df.to_html`, them read it in ? just to give an example of how to do it (i do this with read_csv a little lower in the file)

do a separate PR
 see this:

https://www.travis-ci.org/pydata/pandas/jobs/7320947

I don't think travis was actually testing html5lib stuff....(I just added it in)
its taken out right now

add in ci/install.sh (right after bs4)....and test
 going to put in a separate issue
 ok.
