Add PyPi installation info to README
Add create_readme_rst command to setup.py

This command converts the README.md file to README.rst, so that
the long_description kwarg to setup() has a value compatible
with PyPI.
Add README.rst file, auto-converted from README.md
Fix MANIFEST.in errors
Remove search_field kwarg requirement for non-ajax select2 fields
Fix bug that prevented use of `to_field` kwarg on select2 ForeignKey
Make select2 formfield widgets extendable
Bump version to 1.1.1