Add API endpoint for destroying cookbook versions

:fork_and_knife: Adds API endpoint for destroying a single cookbook version.

Closes #583.
Ah it was actually because I wasn't specifying the `:version` constraint as `VERSION_PATTERN` in the routes, made the change in https://github.com/opscode/supermarket/commit/2ff26d4db71b0cc064e8887a2992d84fdd4e81a8.