Added a method to export form event mappings to Project object.

I created a new method called export_fem in the Project object in
project.py It is almost entirely the same as the  export_metadata
method, except I modified the call to __basepl by specifying
formEventMapping as the content, added the arms key (a list of desired
arm numbers) to and removed fields and forms from the method arguments
and payload, and I modified the call to _call_api to use exp_fem as the
typpe argument.
Update README with new form event mapping info

Added form event mapping export to features list and usage examples.
Fixed form event mapping conversion to pandas.DataFrame and added fem test case.
Merge branch 'master' of https://github.com/aaron0browne/PyCap

Edited readme on web interface to include fem examples.
Merge pull request #14 from aaron0browne/master

Added form event mapping export and associated bits'n'pieces.