[AF10] Money class that handles money

Squashed commit of the following:

commit 81b111228915ca42e6c602c48622b4043bf896ef
Author: Changok Kim <ckim@twitter.com>
Date:   Sun Aug 17 21:35:08 2014 -0700

    add money class in lib and make it available in Fixnum

commit 2dac3827e111222504707e15684a6128a74f0c07
Author: Changok Kim <ckim@twitter.com>
Date:   Sun Aug 17 17:52:51 2014 -0700

    update ruby version and spring