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.
Might be nice to built this and install it into `(share+"test").install` instead? Means the test stage can be a bit faster for e.g. bottles.