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.

Check the file size savings here:

```bash
$ ls -l static/fonts | grep woff
-rw-r--r--  1 mathias  staff  34948 Oct  1 11:21 KaTeX_AMS-Regular.woff
-rw-r--r--  1 mathias  staff  28584 Oct  1 11:23 KaTeX_AMS-Regular.woff2
-rw-r--r--  1 mathias  staff   8372 Oct  1 11:21 KaTeX_Caligraphic-Bold.woff
-rw-r--r--  1 mathias  staff   7312 Oct  1 11:23 KaTeX_Caligraphic-Bold.woff2
-rw-r--r--  1 mathias  staff   8296 Oct  1 11:21 KaTeX_Caligraphic-Regular.woff
-rw-r--r--  1 mathias  staff   7288 Oct  1 11:23 KaTeX_Caligraphic-Regular.woff2
-rw-r--r--  1 mathias  staff  18268 Oct  1 11:21 KaTeX_Fraktur-Bold.woff
-rw-r--r--  1 mathias  staff  16104 Oct  1 11:23 KaTeX_Fraktur-Bold.woff2
-rw-r--r--  1 mathias  staff  17784 Oct  1 11:21 KaTeX_Fraktur-Regular.woff
-rw-r--r--  1 mathias  staff  15508 Oct  1 11:23 KaTeX_Fraktur-Regular.woff2
-rw-r--r--  1 mathias  staff   2904 Oct  1 11:23 KaTeX_Greek-Bold.woff2
-rw-r--r--  1 mathias  staff   7648 Oct  1 11:23 KaTeX_Greek-BoldItalic.woff2
-rw-r--r--  1 mathias  staff   7436 Oct  1 11:23 KaTeX_Greek-Italic.woff2
-rw-r--r--  1 mathias  staff   3036 Oct  1 11:23 KaTeX_Greek-Regular.woff2
-rw-r--r--  1 mathias  staff  28936 Oct  1 11:21 KaTeX_Main-Bold.woff
-rw-r--r--  1 mathias  staff  23816 Oct  1 11:23 KaTeX_Main-Bold.woff2
-rw-r--r--  1 mathias  staff  17576 Oct  1 11:21 KaTeX_Main-Italic.woff
-rw-r--r--  1 mathias  staff  14840 Oct  1 11:23 KaTeX_Main-Italic.woff2
-rw-r--r--  1 mathias  staff  28916 Oct  1 11:21 KaTeX_Main-Regular.woff
-rw-r--r--  1 mathias  staff  23916 Oct  1 11:23 KaTeX_Main-Regular.woff2
-rw-r--r--  1 mathias  staff  16324 Oct  1 11:21 KaTeX_Math-BoldItalic.woff
-rw-r--r--  1 mathias  staff  13988 Oct  1 11:23 KaTeX_Math-BoldItalic.woff2
-rw-r--r--  1 mathias  staff  16580 Oct  1 11:21 KaTeX_Math-Italic.woff
-rw-r--r--  1 mathias  staff  14104 Oct  1 11:23 KaTeX_Math-Italic.woff2
-rw-r--r--  1 mathias  staff  16516 Oct  1 11:21 KaTeX_Math-Regular.woff
-rw-r--r--  1 mathias  staff  14124 Oct  1 11:23 KaTeX_Math-Regular.woff2
-rw-r--r--  1 mathias  staff  13580 Oct  1 11:21 KaTeX_SansSerif-Bold.woff
-rw-r--r--  1 mathias  staff  11084 Oct  1 11:23 KaTeX_SansSerif-Bold.woff2
-rw-r--r--  1 mathias  staff  13140 Oct  1 11:21 KaTeX_SansSerif-Italic.woff
-rw-r--r--  1 mathias  staff  10872 Oct  1 11:23 KaTeX_SansSerif-Italic.woff2
-rw-r--r--  1 mathias  staff  11312 Oct  1 11:21 KaTeX_SansSerif-Regular.woff
-rw-r--r--  1 mathias  staff   9220 Oct  1 11:23 KaTeX_SansSerif-Regular.woff2
-rw-r--r--  1 mathias  staff   9796 Oct  1 11:21 KaTeX_Script-Regular.woff
-rw-r--r--  1 mathias  staff   8700 Oct  1 11:23 KaTeX_Script-Regular.woff2
-rw-r--r--  1 mathias  staff   5724 Oct  1 11:21 KaTeX_Size1-Regular.woff
-rw-r--r--  1 mathias  staff   4632 Oct  1 11:23 KaTeX_Size1-Regular.woff2
-rw-r--r--  1 mathias  staff   5464 Oct  1 11:21 KaTeX_Size2-Regular.woff
-rw-r--r--  1 mathias  staff   4396 Oct  1 11:23 KaTeX_Size2-Regular.woff2
-rw-r--r--  1 mathias  staff   3632 Oct  1 11:21 KaTeX_Size3-Regular.woff
-rw-r--r--  1 mathias  staff   2812 Oct  1 11:23 KaTeX_Size3-Regular.woff2
-rw-r--r--  1 mathias  staff   5268 Oct  1 11:21 KaTeX_Size4-Regular.woff
-rw-r--r--  1 mathias  staff   4032 Oct  1 11:23 KaTeX_Size4-Regular.woff2
-rw-r--r--  1 mathias  staff  14976 Oct  1 11:21 KaTeX_Typewriter-Regular.woff
-rw-r--r--  1 mathias  staff  12272 Oct  1 11:23 KaTeX_Typewriter-Regular.woff2
```