Add support for the AMPL language

The proposed PR adds support for the AMPL language (http://en.wikipedia.org/wiki/AMPL). AMPL is a popular language for mathematical programming (optimization). Currently AMPL code is incorrectly reported as Modula-2 code on Ohloh, see here: https://www.ohloh.net/forums/10/topics/8617?page=1#posts-25355