Update README.md

Configuration examples added.
Fixed typo
Added HydratingResultSet in order to handle $foundOnly param of
MongoCursor::count()
Deprecated AbstractMongoObject::objectExistsInDatabase()
Closes #8
Fixed MongoCursor count() test
Update and preparing for 0.5.0
Deps upgrade
Dependency system changed
Step torwards v0.5.0
Contributing.md
Update CONTRIBUTING.md
Introdution of AbstractActiveRecord [Work in progress]
Cleanup
Fixed default construct param in ClassMethods hydrator
Refactoring test naming and cleanup
Cleanup
Update composer.json
Update composer.json
Update README.md
Updated configuration keys