Improve reqpoquery fetcher.

Use md5 hash as repo_id instead of ad hoc monster I created previsously.
Check for empty response from bodhi.
Introduce alter_pkg_name fetcher option.

This allows listing multiple versions of one package with different names in
various repos. Only 'prefix' and 'postfix' translations supported now, others
can be easily added later.

Fetcher interface has changed to accomodate this change but it should be
harder to break by future changes.
Add repo title support.
Update examples.
Add quickstart section to README.