Create the Tools show API endpoint

This allows access to the information for a specific Tool via the API.

An example request:

     GET /api/v1/tools/berkshelf

This will return the information for the berkshelf tool on Supermarket.

Unlike the rest of the API, this commit commit does not add view level specs. I
feel that the API spec properly tests the signature of what is output via the
API, which, to me, feels like the same expectations as the view specs.
Merge pull request #748 from opscode/tool_show_api

Create the Tools show API endpoint