Rspec's #match_array doesn't check order
Add overhead benchmark
Perfomance optimizations and refactoring.

* cache locale fallbacks and its corresponding columns on a class level
* calculate locale fallbacks list and check if class responds to a
  corresponding method instead of grepping and sorting all instance
  methods
* decouple locale fallback logic from ActiveRecord
* use named module with initialization, like
  `include Traco::Attributes.new(:title)`
Tweaks and cleanup for the nashbridges/performance patch.

Squashes these commits:

Mention benchmark in README, and doc its meaning

Doc LocaleFallbacks API compatibility

Whitespace, code style

Bump version

Code style

LocaleFallbacks/spec cleanup

Don't stub unnecessarily

Don't use described_class

https://github.com/barsoom/devbook/tree/master/styleguide#avoid-described_class

Explicit expectation

Separate spec_helper_models

Clarify spec

Restore locales_for_attribute API

We can add this argument if it's needed and documented.

Flag method as internal

More convenient to keep it public, but it's undocumented and should not be relied on.

Rename to Traco::ClassMethods again

Change (unreleased) version

No new API so it shouldn't have been a minor bump.
List contributors