mpv lua script tweaks
Introduce options 'start' end 'end' in API and tool. Closes #32.

These specify where to start end end the nordlicht. For example,

    nordlicht --start 0.33 --end 0.66 video.mp4

will constrain the nordlicht to the video's middle third.
Remove Vagrantfile and related files

It seems to clutter this project and belongs somewhere else.
Move source files to the top level of the project

They are the main attraction. The Git project does it like this, too.
Remove example file, it probably belongs somewhere else
Fix the mpv-nordlicht.lua script: Start fullscreen after 0.1 sec.
Add "column" style
Allow the specification of a multi-track layout in API and CLI

You cannot spefify the track's heights yet, but this closes #27.
Add 'thumbnails' style, regression to dumb scaling
Refactor main.c
Move start/end information to the video source
Added some const and some malloc-casting
Seek to the beginning of the file for each track
Cache some information about the video
add more detailed licensing information