Merge pull request #36 from andreychuk/master

Add aggregate support to MongoBD
merge baseTest to modelTest
add test for MongoDB.php
add PHP 5.5 test for travis-ci
Update Model.php
Adds DataType to map of loaded classes
Converts MutatorTest to inherit from common base class
Merge pull request #38 from timothy-r/master

Adds DataType to map of loaded classes
Adds tests for Collection::get() handling missing items
Updates test method name and removes empty lines
Adds test for Collection::isEmpty
Adds test for Collection::getIterator
Clarifies test fixture set up
Adds test for Collection::toArray
Updates ordered book collection fixture
Adds test for Collection::has() with a MongoId parameter
Adds test for Collection::has() with a non-existent MongoId
Adds test for toArray with non-numeric indexes
Adds test for Collection::toArray()
Adds test for Collection::offsetGet() with integer param