[CorDebug] Use Microsoft Managed Debugger instead of Native Wrappers.

Notes:
*This is a copy-paste revision.
*It contains csproj fixes so it compiles.
[CorDebug] Use a native mdbg function instead of our defined one.
[CorDebug] Internal API changes.
[CorDebug] Added README for working on this project.
Merge pull request #388 from mono/newCor

[CorDebug] Switch to managed library on top of the debugger.