Move market maker example to examples and make more robust

[0xAlcibiades]

Since the market maker code is not otherwise used in the library, nor the binary in tests, I moved the example to the rust examples directory, and made enhancements to the code. Was doing this to get an understanding for myself of the platform and figured it'd be good to share upstream.

[lmlmt]

Closing - not sure what's being enhanced in the market maker. Would help to get a more specific idea