* Fix various issues detected by megacheck

I've ran honnef.co/go/tools/cmd/megacheck and fixed a few of the
things that came up there.

* Cleanup using Gogland

* documentation: copied old documentation from wiki

* command: better online documentation

Help without arguments prints just a short summary for each command,
help followed by a command prints the command's syntax and a longer
explanation.

* documentation: automatically generate Documentation/cli/README.md