Add WOFF2 versions of the fonts

Contrary to other web font formats, the new WOFF 2.0 Web Font compression format is optimized for file size, memory usage, and decompression speed.

WOFF2 has been supported in Chrome and Opera for a while now. See https://dev.opera.com/blog/opera-23/ for more info.
Merge pull request #142 from mathiasbynens/woff2

Add WOFF2 versions of the fonts
Add the ability to add woff2 files to the docker

Summary:
To complement pull request #142, add the ability to automatically
generate the woff2 files from within the docker. Add a script for copying out
the generated font files to make things easier. Remove the KaTeX_Greek font
files as well as the KaTeX_Win ones, since we don't use them and they're oddly
non-woff and non-eot specific?

Test Plan:
 - Build a new docker from the new Dockerfile
  - Make sure the woff2_compress program compiles
 - Follow the instructions in the README to build the fonts
  - Make sure the fonts correctly build
  - Make sure the copy_fonts.sh script copies the fonts out

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D13637