feature/30c3 and more

As a preparation for 31C3 I implemented parsing of the 30C3 data over last weekend.

In the process I also cleaned up a few things, added a `.gitignore` and streamlined the config a bit.
And then… I noticed that media.ccc.de has an (experimental) API. So I included that as well and added a definition for the previously undefined `enclosures` and added a `subtitle` to sessions. And updated the docs, of course.

So all in all we have:

- (A little bit) simpler config and usage
- Added `.gitignore` so npm install does not mess up the tree
- Added `schedule.xml` and `person.json` import from Pentabarf for 30c3 (but could be used for many pentabarf based conferences with a little abstraction)
- Added support for `media.ccc.de` API to import MP4 videos as enclosures
- Defined the `enclosure` field. It can now represent a recording, slides or even a live stream (think HTTP Live Streaming)
- Added a `subtitle` field for `session`
- Added docs for the above, also started documenting required and optional fields

So I realize this goes beyond what should be in one PR, but considering my limited time ATM I thought it could be tested and reviewed as one big thing as I consider it an improvement.