Add Forth extension .fr

GitHub hosts at least 18000 files with the `.fr` extension.  They are currently detected as `Frege`.  (Most of those seem to be plain text with strings in French.)

However, about 240 are actually in `Forth`:
http://github.com/search?q=extension%3Afr+dup+swap

This pull request adds `.fr` as a Forth file extension, and an `asm.fr` sample.  The Bayesian classifier seem to do really well.  In the repositories below, and there were only a handful of misclassifications.

Tested with:
http://github.com/Frege/frege
http://github.com/cataska/ficl
http://github.com/jamesbowman/forth-ans
http://github.com/andrewtron3000/embedded-ml