Fixed null ref in Library.ToString()
- Print no version if version is null

#249
Fixed duplicate assembly registration on mono
- Overwrite assemblies registered by name when finding reference assemblies.
- Also set the path of the framework directory

Fixed #252
Implemented IApplicationShutdown
- When files change RequestShutdown waiting for the debugger to detach.
Removed unused project.json
Small refactoring
Changed IAssemblyLoaderEngine.LoadBytes to LoadStream
- Optimized for CoreCLR scenarios
- Desktop CLR will convert to byte[]