Binary format specs generation

[roosmaa]

I was looking into signing payment transactions on the client side and kind of went down the rabbit hole to also look into the binary protocol in more depth.

If I understand correctly, then the update_binformat.js is used to generate the binformat.js in stellar-lib. As comments in update_binformat.js bring out, doing this using RegEx is not very elegant approach. It works, but it doesn't scale - hard for others to generate something for their platform/language of choice.

To encourage the creation of clients (or even alternative server implementations) I think stellard could spit out the protocol specs in a consistent format from which libraries for other languages could be generated. Or better yet, hand maintain the specs and generate the C++ code which stellard itself can use. (C++ pre-processor magic could work nicely, kind of like in SerializeDeclarations.h)

What do you think? Think this ties into #124 as well.