Compile dependency container with declared getter for each service

This adds a class and minion task that can compile a Dependency_Definition_List to a custom class providing getters (with appropriate phpdoc return tags) for each defined service. This allows for IDE autocompletion and usage tracking for easier refactoring. It also creates all services as part of the compile, providing a quick way to validate that the dependency configuration is correct (or at least correct enough that it doesn't blow up with incorrect arguments or missing nested dependencies).

As the module so far has no tests, I've added a travis build configuration and phpspec (which is our preferred BDD tool at the moment) for the new class.

@Zeelot no worries if you feel this (either the compiler or the phpspec) isn't right for you, we can maintain it as a separate package if required.