remove requirement on 'store' reports

Parsing the YAML file generated by the 'store' report processor is a
bit dumb, as we already have all the information we need in `self`.

This simplifies the `last_report` method by removing the most fragile
part, and removes the dependency on the 'store' processor.
reorganise message generation

It's no longer either gists or local reports. You can have both
together, in a slightly longer line, if you wish.
Add report URL to IRC messages

This adds the ability to define an URL for each report, optionnally
substituting string sequences with values from the report.
restructured configuration documentation
Merge pull request #8 from mfournier/remove_yaml_parsing+add_url_support

Remove yaml parsing+add url support