Better documenation

[wader]

Feedback and ideas:

• Don't use name/arity notation for functions unless it needed. Use name, name(arga; argb) instead
• Add some basic functions/syntax help to --help
• Inline documentation in go and jq source, extract it and generate documentation. Maybe use https://github.com/fadado/JBOL/blob/master/doc/JQ-Distilled.md#type-signatures and then render more user friendly versions?
• More examples

[Doctor-love]

#110 partly solves this issue

[wader]

In master all documentation is in markdown now again