Add Bob Michael's Toydecoder classes

The toy decoder pieces are in a new oodecoder subdirectory (in parallel with src, hana_scaler, and hana_decode).

A parallel structure is maintained with existing Hall A code.  The toy decoder can either be built with the Makefile in the oodecoder directory, or with scons using "scons standalone=1".

Also add a README for installing and using Eclipse with SCons and PyDev plugins (as well as Git and GitHub!) on MacOSX (although it should apply to any operating system, in principle).