plenty changes for 2.0
use NaN for empty cache size
make sure tests have close to 100% coverage
optimize cache searching
dict.items is not generator in python2.x
we also tested against Python 3.4
bugfix when inserting empty document
add testcase and comments
optimize insert_multiple
Revert "optimize insert_multiple"

This reverts commit 0d0d77edc26c88934a52cf88fb4b4447686ad00d.
Merge branch 'master' into 2.0
Merge branch '2.0' of https://github.com/eugene-eeo/tinydb into eugene-eeo-2.0

Conflicts:
	README.rst
	tinydb/middlewares.py
Merge branch 'eugene-eeo-2.0'