Added topic coherence rst files

[devashishd12]

Referring to issue #905. @tmylk just a small addition here.

[devashishd12]

I'll add the topic coherence dir as well here.

[devashishd12]

@tmylk ready for merge.

[tmylk]

Thanks for taking this on! Did you check that html files appear after running the commands in https://github.com/RaRe-Technologies/gensim/wiki/Developer-page#documentation?

[devashishd12]

oh getting an error there:

Exception occurred:
  File "/home/devashish/EXPERIMENTATION/gensim/docs/src/./gensim_theme/genindex.html", line 49, in block "body"
    {%- for entryname, (links, subitems, _) in column %}
ValueError: need more than 2 values to unpack
The full traceback has been saved in /tmp/sphinx-err-eVoHAI.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!
Makefile:34: recipe for target 'html' failed
make: *** [html] Error 1

[devashishd12]

updated to Sphinx 1.4 and now it builds fine. Sorry for the noise!

[tmylk]

Thanks for the PR!

[devashishd12]

No problem! The topic coherence docs look hideous currently. Will improve on that soon.