Bulk Resource Management

[danielgtaylor]

This PR adds support for client-side bulk resource management via a git-like interface behind the new restish bulk subcommand. Typical usage:

$ mkdir books && cd books
$ restish bulk init api.rest.sh/books

# ... Make changes ...

$ restish bulk status
$ restish bulk diff

$ restish bulk push

This works for any API which returns a list of versioned resources which either include links to fetch each resource, or have enough information to generate links from a template. Lots of docs are included so I'll let those stand on their own and not repeat everything here!