Missing CoreCompile bug

No more "The target "CoreCompile" does not exist in the project." on
packaging projects.
v2.3.0-a1

- support for XML doc file #54
- minor refactor of AssemblyReader #53

a1, because Windows Phone support is still not finished, issues:
- serialization exception during VS2010 build
- automatic dependency calculation screws up with mixed SL40WP7x project
types