support for msgpack

[alec-c4]

Hi, guys.
Could you please add support for msgpack (http://msgpack.org) in grape? I've found https://github.com/rosylilly/grape-msgpack, but i think it will be better to have msgpack support as part of grape.

[mbleigh]

@dblock your call, but my vote would be 👎

In general there are already things in Grape that I'd prefer we break out into separate gems, so I'm definitely not interested in adding more dependencies to the core lib.

[dblock]

I agree with @mbleigh, we want Grape to be more modular vs. less modular as it grows. I'd love a PR that talks about msgpack support in README though, please?

[purezen]

You mean, a link to the grape-msgpack repo? @dblock

[dblock]

See, I didn't know about https://github.com/rosylilly/grape-msgpack :) So yes, feel free to call that out the same way we talk about ActiveModelSerilizers for example.