Read html with colspan rowspan
 - [x] closes #17054
 - [x] tests added / passed
 - [ ] passes ``git diff upstream/master -u -- "*.py" | flake8 --diff``
 - [ ] whatsnew entry

There's a parsererror include in the test file that doesn't need to be there any more since I removed the test.

whatsnew entry:

`read_html` now:
- handles colspan/rowspan in table elements
- attempts to infer table headers in the absence of `<thead>`
@jowens : Yikes!  That's a pretty massive diff.  Let's rebase onto `master` first so we can have a better idea of what you're actually changing. Please help me with the rebase. I thought I'd done it right ...

```
 9847  git commit -m"read_html handles rowspan and colspan in tables, infers headers if <thead> is not specified" pandas/io/html.py
 9848  git commit -m"added rowspan/colspan/infer-header tests. removed test_computer_sales_page, which now appears to parse correctly." pandas/tests/io/test_html.py
 9849  git rebase upstream/master
 9851  git rebase -i HEAD~2
 9852  git rebase -i master
 9853  git push origin html_read-handles-colspan-rowspan-and-infers-headers -f
 9854  git push origin read_html_with_colspan_rowspan -f
 9855  git push origin read_html_with_colspan_rowspan
``` FWIW, I changed exactly two files. @jowens : Save the commit hashes of your two PR commits and then do the following:
1. Update your origin `master` branch to match `upstream`.
2. Once they are even, on this PR branch, run `git reset --hard origin/master`.
3. Then for each commit hash, perform `git cherry-pick <hash>`
4. Push to your PR branch

Let me know if you have any questions! @gfyoung you have the patience of a saint. I don't know what went so wrong that I'm having all this trouble merging; I'm tempted to just start over with a clean branch. Anyway, for your step 4, can you help?

```
$ git status
On branch read_html_with_colspan_rowspan
nothing added to commit but untracked files present (use "git add" to track)
...
$ git push
fatal: The current branch read_html_with_colspan_rowspan has no upstream branch.
To push the current branch and set the remote as upstream, use

    git push --set-upstream origin read_html_with_colspan_rowspan

$     git push --set-upstream origin read_html_with_colspan_rowspan
To github.com:jowens/pandas.git
 ! [rejected]            read_html_with_colspan_rowspan -> read_html_with_colspan_rowspan (non-fast-forward)
error: failed to push some refs to 'git@github.com:jowens/pandas.git'
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Integrate the remote changes (e.g.
hint: 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.
``` My history, for posterity. I tried to follow your directions, but my git experience doesn't involve pull requests in this way.

```
 8954  git pull upstream
 8956  git checkout upstream
 8957  git checkout master
 8958  git fetch upstream
 8959  git checkout read_html_with_colspan_rowspan
 8960  git reset --hard origin/master
 8961  git cherry-pick b922af71bc606aa207cda0725990204b47f4e24f
 8970  python setup.py build_ext --inplace
 8971  py.test-2.7 pandas/io/tests/test_html.py
 8974  git cherry-pick --continue
 8975  git cherry-pick 5818f804b0ce99cecbb7ae079764a634e69ab8e4
 8976  git pull
 8977  git pull origin/master
 8978  git pull master
 8979  git pull origin
 8980  git cherry-pick --continue
 8981  git status
 8982  git push
 8983      git push --set-upstream origin read_html_with_colspan_rowspan
``` Should I just start over? It'd surely save you a lot of effort. > Should I just start over? It'd surely save you a lot of effort.

Whatever is easiest for you.  I'm here to help you through the process so that we can get beneficial contributions like yours merged.

Also, at your last step, you should run:
~~~
git push -f --set-upstream origin read_html_with_colspan_rowspan
~~~ Hello @jowens! Thanks for updating the PR.





Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on July 26, 2017 at 23:16 Hours UTC Ah, the mysterious `-f`.

This has now been pushed. What next? You're awesome, @gfyoung. OK, I'm gonna start over. Stay tuned! > OK, I'm gonna start over. Stay tuned!

I'm confused...why are you starting over? > Ah, the mysterious -f.

This means push your version of the branch to `origin`, overwriting whatever was there previously.  Thus, it doesn't care if your branch was behind its remote counterpart. (`-f` = `--force`) I started over because even after doing a second round I had merge conflicts, and so starting over seemed most sensible in terms of my time. This round went better. https://github.com/pandas-dev/pandas/pull/17089 Okay, closing this then.