Rename -v => -d , fixing App#refresh_loop to reraise if DEBUG.

Verbose mode `-v` is actually better described as debug mode `-d`, as
it also explodes with stack traces if enabled. It is intended that the
option is not used generally, so transient errors will be ignored and
the operations retried when running with `--eternal`. Also fix
`App#refresh_loop` to reraise stack traces when running in debug mode.

When using the `bin/ryespy` executable in development, you'll probably
want to set this `--debug`,`-d` mode.
Implement Listener::GoogCS , for Google Cloud Storage.

The `GoogCS` listener listens to one or more file key prefix filters in
a Google Cloud Storage bucket, looking for new or changed files.

The implementation is almost identical to `Listener::AmznS3`. At least
for now, the listeners are handled fairly separately, however, to allow
for any service-specific tweaks. c.f. `Listener::RaxCF`, which needs
a specific treatment for authentication endpoints and regions.

`README` and `ryespy.gemspec` are updated to document usage and the
extended utility of Ryespy.

This listener is fully functional.
Refactor Listener::AmznS3,GoogCS,RaxCF , extracting #redis_key .

Rename `@cf_config` => `@config`. Rename `#connect_fog_storage` =>
`#connect_service`. Extract `#close` to `Fogable`. Extract
`AmznS3#redis_key`,`GoogCS#redis_key` to `Fogable#redis_key` (note that
`RaxCF#redis_key` is significantly different).
Refactor Listeners to Listener::Base .

Create `Listener::Base`, from which all listeners inherit. Move
`Listener::Fogable#close` => `Listener::Base#close`. All listeners
should call `super(opts)` within `#initialize` and define a
`#connect_service` as appropriate.

Document need to `require 'ryespy'` in `README`; this should probably
have been included before. :)