Ignore rbenv version files.
Remove the JSON_FORMAT mapping.

Refactor out the JSON_COMMAND array and require commands to be passed
in as an array so that we can support an options has that includes a
:format key that defines the requested return format.
Nuke unused Request#execute! method
Add Switch#run! convenience method

Adds a run! convenience method for running a single command and getting
the result back.
Bump version number thanks to breaking API changes.