Reference dlls in root of build directory

Improves compatibility with different configurations, but at the cost of
requiring some more initial configuration from the developer.
Run xbuild/mono/rm in separate console window

Fixes building on Windows
Add .gitignore
Add build instructions for Windows to README
Fix clean command on Windows
File deletion in windows
Release config should match debug config
Delete Assembly-CSharp.dll before running ILRepack

Ensures modloader is correctly rebuilt without doing a full rebuild
Fix release build target

Also alters debug building to use the ${ProjectConfig} variable
Merge pull request #1 from ahockersten/windows_compile_fixes

Windows compile fixes
Fixed for latest version. Bug fixes. Slightly modified mod API.