Asgrim's refactorings

Todo:

* Update mimmi20/WurflCache when mimmi20/WurflCache#1 is merged
* `browscap:fetch` command MUST check the version vs the downloaded to avoid hitting download limit
  * The default behaviour should be to check the current version vs browscap.org/version-number - if we are up to date, just print a message saying the local file is up to date.
  * We should implement a force flag to override this behaviour just in case someone DOES want to re-download for whatever reason, e.g. `bin/browscap browscap:fetch --force`
* I think having the `browscap:` prefix is unnecessary? Perhaps remove this