doc: Add map_v4.ksy

- Parses all non-extension item types
- Parses quads, sound sources
- Parses envelope points, although you manually have to click ddnet/teeworlds07.
I didn't find a way to pass the envelope version there

Potential TODO:

- Add doc strings to item attributes
- Support more extension item types 
(its hard to calculate their id with the id<->uuid mapping,
maybe differentiate with item length?)
- Parse tile data

For now, I'm just happy that I got it into a nice, usable state.
Feel free to improve this file

Author: Patiga