Setup should use `https://github.com/CocoaPods/Specs.git` url

See #324.

The specification class only stores the active platform symbol.

* ticket-291:
  [TargetInstaller] Integrate with Xcodeproj f0d455bcd8.
  [TargetInstaller] Add source files in batch.

Support for `header_dir` attr in subspecs.

Introduced Chameleon fixture.

The change is small refactoring to make clear which methods
return relative paths.

* master:
  List all the specifications of a local pod.
  Improve error message for missing local pod. Closes #323.

[Platform] Require a name on initialization

Closes #305.