Also made the C# implementation support unsigned types, and
made it more like the Java version.
Bug: 17359988
Change-Id: If5305c08cd5c97f35426639516ce05e53bbec36c
Tested: on Linux and Windows.
Include C# codegen in flatc and .NET FlatBuffer access via the
FlatBufferBuilder class
Tested: on Windows.
Change-Id: If5228a8df60a10e0751b245c6c64530264ea2d8a