Initial support for vendors.
Install nut into <prefix>/<vendor>/<name>.
Update documentation.
Update spec.
Add usage examples.
Use vendors in `nut publish`.
Test nuts moved to debug vendor.
Call prepare_test.
Fix test skipping.
Fix -h handling, add version to help.
Check for extra arguments.
Export main.Config, change meaning of GONUTS_IO_SERVER.
Get token from config.
Simplify tests.
Nut.ReadFrom()
`nut get`: print error.
Spec.ReadFile()
Check NutFile interface too.
Refactor.
NutFile.ReadFile()