Added 'X-Clockwork-Path' header check

The X-Clockwork-Path header can change the base URL that Clockwork will
check for request JSON. If present it will be prefixed to the already
standard /__clockwork/{id} URL. For instance passing
/some/directory/path in X-Clockwork-Path will then have the request be
/some/directory/path/__clockwork/{id}.
X-Clockwork-Path now overrides default '/__clockwork/' uri, instead of prefixing.
Bumped the version to 1.1, updated changelog and todo.