Add "kpm add" command
Separate pack exclusion from compile exclusion
Added support for precompiled binaries and refactored some stuff
- project.json can say (per target framework), what the behavior should be.
- Made IProjectExportProvider return the specific IMetadataProjectReference instead of the closure
- Added CompiledProjectMetadataReference for already compiled projects (or to consume output from
 other projects)
Updated to handle roslyn changes
Revert "Updated to handle roslyn changes"

This reverts commit 46bebbccd3244f68931f84a1f33ae3231442c39e.
Use Console.Error for printing out errors from BuildManager
Fix KRE lookup path in .cmd files generated by "kpm pack"