Merge pull request #339 from petrus-jvrensburg/docs

Docs
Doc updates
Update MongoEngine filters.py to include options descriptions similar to BaseFilter

BaseFilter properly describes use of options. Including same wording for mongoengine filters.py
Merge pull request #340 from rturk/master

Update MongoEngine filters.py to include options description similar to BaseFilter
Add Installation ans Testing sections to README.
Change some wording in the README.