create_indexes should not fail when cannot constantize class [Fix #2758]

rake task db:mongoid:create_indexes should not fail if the name of the
file doest not match the class name
Ensure positional operator use in embedded inserts.

[ fix #2769 ]
Update changelog
Merge branch 'pr/2768'
Jruby build should run
Enumerable.matching_document _unloaded double query fix

When there was a many to many, and the target was not loaded and target.first was called, _unloaded was calling the db twice in order to load
Dont clear persistence_options when _loading_revision [ Fixes #2743]
Update changelog
Update travis with max size
 should support _ids of type hash, array etc.
Update changelog
Remove c extension opts
Fixing spec for jruby
Fix usec rounding errors on JRuby and MRI.

[ fix #2741 ]
Don't persist non new child docs with nil inverse.

[ fix #2733 ]
Give access to validations on the instance level.

[ fix #2774 ]
adding counter cache #2214

Example:

  class Person
    include Mongoid::Document
    has_many :pets
  end

  class Pet
    include Mongoid::Document
    belongs_to :person, counter_cache: true
  end
Slight refactor and changelog update
Allow eager loading from embedded documents.

[ fix #2662 ]
Cleanup excessive db queries in 1-1 relations.

[ fix #2701 ]