Rename the 'redcap' backend module to redcap_mysql.py

This is more explicit and prevents conflicting with the PyCap
library for API-based access.
Implement backend for the REDCap HTTP API

This requires PyCap
Implement backend for REDCap data dictionary CSV files
Change backend name for redcap_mysql to 'redcap-mysql' and add alias

The 'redcap' backend still points to the redcap-mysql backend, but
the native backend name is now more explicit to differentiate itself
from the api and csv versions.
Extract additional field metadata in redcap-mysql backend
Add REDCap iPython notebook examples

Links to viewable version in README