First alpha

Totally the first prerelease of repocribro! There are still some things to finish in order to fullfil the initial specification it the README file:

• add more hooks and improve extensibility of core application (and document it),
• procedure to checking missed repository events from webhooks (as CLI command),
• fix few minor bugs and do some improvements.

There should be also provided documentation of the code (docstrings) and more tests for the next goal, the v0.1 release.

Hope it's just a first step on a long and interesting path of this project.