Fix the type spec for ExMake.Utils.ignore/1.
Support :silent/:ignore option arguments to ExMake.Utils.{shell/2,find_exe/3}.
Add an initial C# library.
Add an initial F# library.
C#/F#: Pass -nologo/--nologo to suppress compiler copyright message.
C#/F#: Key containers are names, not files, so no need to special case them.