configuration
-------------

- `fragment` (`str`): path to GLSL fragment shader.
- `width` (`int`): horizontal rendering resolution. defaults to `1920`.
- `height` (`int`): vertical rendering resolution. defaults to `1080`.
- `outputs`: list of outputs. defaults to one 800x600 window.
  each output is a dictionary with the following keys:
  - `type` (`str`): currently always `window`.
  - `width` (`int`): window width. defaults to `800`.
  - `height` (`int`): window height. defaults to `600`.
- `osc`: either a 'liblo URL' or dictionary with the following keys:
  - `protocol` (`str`): `udp`, `tcp` or `unix`. defaults to `udp`.
  - `port` (`int`): port to bind to. defaults to `9000`.

### libio URLs
Unfortunately undocumented by libio. The following formats are valid:

- `osc.udp://localhost:1234`
- `osc.udp://224.0.1.9:1234` (multicast IP)
- `osc.tcp://:1234`
- `osc.unix://localhost/tmp/mysocket`