Refactored the assembly loaders
- Simplified IAssemblyLoader.Load
- Added more types to the service provider so that
  the RoslynAssemblyLoader can be type activated with the service provider
- Made IFileWatcher assembly neutral
- Renamed LazyRoslynAssemblyLoader to ProjectAssemblyLoader
Split project export resolution into the core
- Made ProjectExportProvider which is an uber ILibraryExportProvider that
  returns an ILibraryExport for the entire project based on the
  specified target framework.
- Added IMetadataRawReference which reflects assembly metadata as a byte[]
- Made EmbeddedMetadataReference implement IMetadataRawReference
- Simplified roslyn compiler logic by using the new ProjectExportProvider as
  part of the compilation process.
- Improve tracing in ProjectExportProvider
- Pass the ILibraryExportProvider to GetProjectExport
Fixed active target framework for compilation
- ProjectExportProvider now returns the effectiveTargetFramework in
  an out parameter.
- The RoslynCompiler uses this as the effective target framework for
  compilation.
fix build.sh on XDG_DATA_HOME and copy nuget.exe

The correct way to verify the variable is using -z.
To copy a file on bash you need to specify the filename also, not the
folder only.
Added execute permission to build.sh.
fix build.sh to use wget -O instead of -o