Adds quality spec

  - Runs with: rspec spec/quality_spec.rb
Added error message: can't mass assign protected attribute
add to_mongo/from_mongo to Symbol
Added ability to pull stats on a class

  Since going through the collection API is a bit awkward and the keys
  returned are camel-cased, this commit adds the ability to get these
  stats through ClassName.stats.snake_cased_field.
Fixed be_true -> be_truthy deprecation warning in specs
Fixed be_false -> be_falsey deprecation warning in specs

  Used the follwoing command to do this:
  $ grep -R be_false spec/ | awk -F: '{print $1}' | uniq | xargs sed -i 's/be_false/be_falsey/g'
Fixed other rspec depprectations (its)
Add counter caching.
counter caching: Add more conventional syntax: belongs_to :association, :counter_cache => true
Fix remove_validations_for for AS 4.1

This is a slightly reworked version of the @fcheung's pull
request #584, using the same method across ActiveSupport
versions.  I added a definition for `set_callbacks`, which is
present in AS 4.1 but not in earlier versions.  This can be
discarded once older versions of AS are no longer supported.
Fix remove_validations_for fix for AS 3.x/4.x
Merge pull request #587 from cpmurphy/fixes/keys_active_support_4_1

Fix remove_validations_for for AS 4.1
Merge pull request #583 from sgnn7/add_collection_stats

Add collection stats and cleanup deprecation warnings
Merge pull request #556 from rthbound/adds_quality_spec

Adds quality spec
Merge pull request #581 from miyucy/add-symbol-extension

add to_mongo/from_mongo to Symbol
Merge pull request #558 from ThomasAlxDmy/explicit_error_message

Added error message: can't mass assign protected attribute. This should be deprecated for proper protected_attributes support down the road.
Merge pull request #586 from smtlaissezfaire/counter_cache

Counter cache
Add counter caching.
counter caching: Add more conventional syntax: belongs_to :association, :counter_cache => true
We don't support rspec 3 yet.

Revert "Fixed other rspec depprectations (its)"

This reverts commit b25f18d1cf77dfe0a96cd3d01c30a21e093b77c1.

Revert "Fixed be_false -> be_falsey deprecation warning in specs"

This reverts commit 11a512abf822c1db912ba777b387c519cb9e0f22.

Revert "Fixed be_true -> be_truthy deprecation warning in specs"

This reverts commit d6bc31ef7b179d57ff0dd47c84bc83bb940be98f.