Allow for exclusion of fields using projection

projection: {‘field’:0} will return all fields except ‘field’. Assumes
projection is properly formatted (either all ‘1’ or ‘0’). Tests
expanded in test_get.py.
Allow factory pattern for creating applications

Only call init_app if app is passed to __init__ function. This allows
for initialization after app instance is created (e.g. factory pattern
for application generation).
Documentation for app factory initialization
Documentation for app factory initialization

Shortened the example code block and added it to README.md. Not sure
how index.rst is working (I’ve never used sphinx), but updated that
documentation too.
Merge pull request #8 from kcaylor/master

Allow for exclusion of fields using projection