corlib and JIT updates

[ncave]

@SteveSanderson

Here are a few fixes and updates to the corlib and JIT:

• Better C# support (added some missing JIT features, some bug fixes and updates).
• Added F# support if needed (uses custom FSharp.Core, see here for a working example).
• Tried my best to keep the corlib light, it's still around 250k (in release mode).
• Release build assemblies now work too (after JIT bugfixes).

I see you added CLR debugging in the browser, that's awesome!

[SteveSandersonMS]

Thanks for submitting this, and for resolving the merge issues with the latest debug-enabled code!

If it's OK with you, I'm moving your PR back over to the other repo. That's because this repo in the aspnet org is even more experimentally-experimental, and won't be maintained over time.

I think the steps from here are:

• I'll selectively merge the commits from this repo (under the aspnet org) back to the one on SteveSanderson. Specifically, the features and commits that are sufficiently complete to be maintained without causing trouble.
• Then I'll merge your PR onto the result of that

[SteveSandersonMS]

Converted to a PR here: SteveSanderson/Blazor#6

[ncave]

@SteveSandersonMS Thanks, let me know if anything in the code is not self-explanatory.