- rename it to Roslyn.Compilers.Extension so it's clearer what it is
- remove the old specification of binding redirects. Now that Update 1
  provides us with the ability to patch the language services with
  a proper VSIX, we don't need to redirect anything other than the build
  task anymore.
- update the set of deployed binaries to the current compiler set
- clean up package code and registration

With Visual Studio 2015 Update 1 you should not specify -anycpu
in the runtimes section. Right now we'll have both to allow us to build
with and without Update 1, and we'll remove the old ones once we've
made the transition.

Update 1 also tries deploying implementations for some class libraries,
so I'm updating all our test and VSIX deployment class libraries to
now include implementations.

Updating System.Reflection.Metadata to 1.1.0-alpha-0015 and System.Collections.Immutable to 1.1.37.0

Revert "Updating System.Reflection.Metadata to 1.1.0-alpha-0015 and System.Collections.Immutable to 1.1.37.0"

This reverts commit d78dbb97.

Updating System.Reflection.Metadata to 1.1.0-alpha-0015 and System.Collections.Immutable to 1.1.37.0

Updating Microsoft.DiaSymReader to v1.0.6, Microsoft.DiaSymReader.Native to v1.2.0, and System.Collections.Immutable to v1.1.37