Adding some internal code to the EventMap class, which was to be used for...

Adding some internal code to the EventMap class, which was to be used for mapping phone-sets -- this was created for something I now won't be doing, but the internal code may be useful in future so I'm committing it.

git-svn-id: https://svn.code.sf.net/p/kaldi/code/trunk@2495 5e6a8d80-dfce-4ca6-a32a-6e07a63d50c8