Adapter Factories

Provides a mechanism to register adapter factory closures to the Environment. The closure accepts an Environment instance as a parameter and should return an object which implements `AdapterInterface`.
The default three adapters are added in the Environment constructor, though it could be easily moved outside of the Environment entirely.
Moves the default adapter factory definitions from the constructor to a static method.
Removes a 'callable' type hint to be compatible with PHP 5.3.
Adds a 'callable' check on AdapterFactory registration.
Fixes the adapter configuration access of options.
Adds documentation explaining the custom adapter behaviour.
PSR2 compliance.
Adds test coverage for the adapter factory closures.
Merge branch 'feature/adapter-registration' of https://github.com/cyrusboadway/phinx into cyrusboadway-feature/adapter-registration

Conflicts:
	src/Phinx/Migration/Manager/Environment.php
remove empty line
dont break php 5.3
more php 5.3 fixes