new formula: opengrm-thrax

OpenGRM-Thrax allows the user to compile morphological analyzers and
context-sensitive rewrite rules into OpenFST finite state automata.

I have not added this to `science` since neither OpenFST (on which it
depends) or OpenGRM-ngram are in `science`. It is at least as practical
as the other two.

Upstream has recently updated, which should solve some of the problems
of prior PRs for this package.