An effort at a small front-end for xbrpc.

This is a work-in-progress that I work on sparingly.

TODO:

• Add more data types as arguments (char, bool, etc.) even though most of these can be achieved with the existent ones (due to how they're given to argument registers anyway).
• Clean up the source of xbrpc and merge it into this repository.
• Add return type information (requires defining a more serious protocol).
• Potentially add length-prefixing to the protocol since right now I'm relying on fairly consistent TCP windowing sizes.
• Add support for an XBDM-based debugging channel that spews everything given to DbbPrint (see https://gist.github.com/obscurecolin/83cda0f6320cba468d3b469a95abaa93 - requires I print useful messages from xbrpc).
• Add tab closing support that actually terminates the connection (kDisconnect)