Adding formula for Hal Daumes machine learning tool

megam and megam.opt (the optimized version) are machine learning commandline tools
used by Python NLP Toolkit (nltk) if the built in libraries are too slow.
Fixed issues spotted by Mike - using Formula["objective-caml"].lib - usings arguments instead of string for system() - Removed generated comments - using file.write << EOS.undent
megam: add src bottle.