Merge branch 'master' into develop
Fix reST markup on CHANGELOG.rst
Optimizes 16MB test (generating less objects)
Updates tox (Python 3.3) and adds .env to ignore
Removes mapping tests from test_mongodict.py

Only MongoDB-related tests remain
Adds Python's mapping tests

Added mapping_tests.py from Python 2.7.5 and Python 3.3.2 source and created
tests/test_mapping_protocol.py to use it to test MongoDict.
Modifies README with information about codecs
Improves pickle test
Add details about Python versions to README
Updates version to 0.3.0
Adds data migration script

This script is needed since value data is not encoded using pickle for
mongodict <= 0.2.1
Updates log of changes between versions
Merge branch 'release/0.3.0'