C# Gremlin Language Variant

It would be nice to have a C# GLV that runs under .NET Framework 4.5+ and .NET Core.

The maven build could use the Exec Maven Plugin to exec .NET Core's dotnet test command.

Some requirements, from the mailing list (edited):

1. The GLV should keep in line with class/method names of the java API
where possible to ensure consistency of feel across languages.
2. There needs to be adequate tests (we're still discussing the approach to
testing GLVs and i think that needs to be tackled sooner than later as more
GLVs start to come in). Those tests should produce xunit style output
unless there is some good reason not to.
3. There needs to be adequate documentation (e.g. Reference docs)
4. The build/deploy process needs to be bound to maven which might be one of the trickier bits to deal with.