Flow correct compilation options in Roslyn compiler to Roslyn parser
Use the same parseOptions for GetSyntaxTrees and for ApplyVersionInfo
Added frameworkAssemblies support
- The frameworkAssemblies section is specific to a target framework
- Refactored BuildContext to call into the ProjectReferenceDependencyProvider.
This means that only a single place actually uses the project class directly
(which is nice).
- GetLibraryDescription now takes a Library instead of name and version
(we may need to revisit this and create a different poco). When @lodejard finishes
dependency types we'll see how this ends up
- Preserve the backwards compatibility of declaring frameworkAssemblies in
dependencies temporarily
- Added tests for parsing frameworkAssemblies

#640
#619
Assume any reference resolved by the framework resolver is a framework ref
Skip framework assemblies for aspnetcore50
Fixup the dependency version when resolving GAC references from the project.
Remove wildcard from the global.json lookup
Don't close the stream when caching metadata references
- Keep the stream open until we dispose the metadata itself
- Change the cache to dispose entries if the old value is disposable
Removing dependencies from shared project
Revert "Removing dependencies from shared project"

This reverts commit 6c29dabe3656b6f3a9fafa279355eb3b742ede61.
Ensure outputDir is never null for packing
Init Win7PlusCoreSystem
Convert to byte[] before creating the image reference for project refs
Skip the check for the things already marked as framework references.
- This will make the "not having VS installed" work the default, implicit
references. But it won't work generally. This fix is good enough since
new code will require the frameworkAssemblies section.

#669
Don't make the default hidden dependencies implicit
Fixup nuspec files on restore if the target nuspec doesn't match case

#664
Remove nuspec file from sln and added global.json
Updating comment
Disable crossgen tests for now.
Reduce number of files in packed output

- Nupkgs, nuspecs and SHA files are not copied to output packages folder
- Only copy assemblies needed by the frameworks being packed with
- Use frameworks in project.json if '--runtime' was not specified
- Use values of '--runtime' to filter frameworks in project.json
- Use SHAs from global.json when resolving KRE_PACKAGES_CACHE
- Copy tools dlls from source packages to bin folder of output