Moved APISpecification to its own file
Moved DependencyConflict to its own file
Moved DependencyRequest to its own file
Moved ActivationRequest to its own file
Moved APISet to its own file
Moved IndexSpecification to its own file
Moved IndexSet to its own file
Moved CurrentSet to its own file
Moved ComposedSet to its own file
Alphabetize methods in DependencyResolver
Moved DependencyResolver exceptions to exceptions.rb
Undent dependency_resolver.rb, fix namespaces
Alphabetize DependencyResolver
Moved GemDependencyAPI to its own file
Undent RequestSet
Alphabetize RequestSet