New formula: opengrm-thrax

The OpenGrm Thrax tools compile grammars expressed as regular
expressions and context-dependent rewrite rules into weighted
finite-state transducers using OpenFST.

The formula includes a patch reported upstream. It simply comments 
out the initialization of a never-used variable.

The test shows conversion of cardinal numbers (like `170`) to word
strings (like `one hundred seventy`). Another potential use is word 
tokenization.

If accepted this would complete the OpenFST/OpenGRM suite.