New addition: Chromatic numbers!

[joshuaguerin]

Updates:

• Added a modified version of the chromatic numbers implementation by @gonz9032. Now doesn't need an input parameter, and added some count macros to clean up the presentation a bit.
• Updated the README to include information about both versions (k-colorability and chromatic numbers).
• Updated the primary README to add chromatic numbers as a table entry, linking to the colorability repo.
• Fixed a minor typo in the table where "First Header" and "Second Header" were still there from templating the table.

[joshuaguerin]

Still not certain what sort of merging we will be using. I'm leaning towards either a squash or rebase.

[gonz9032]

Everything looks good to me!

[joshuaguerin]

OK, I think things are good enough for inclusion for the moment. I'll merge, and we can do a more thorough review of everything later.