KDoc: drop "-docOutput" CLI argument

It was never supported in kdoc-cli. It is still supported as an argument in
kdoc-maven-plugin
(TODO drop -tags?) CLI: add an extra MessageRenderer parameter to compiler exec

Is supposed to be used instead of the "-tags" CLI argument
CLI: output relative paths in diagnostic messages
(TODO test -D, support Win) CLI: support -D and -J, don't pass them to Kotlin compiler
CLI: don't fail on a wrong "-script" usage
CLI: introduce alias "-cp" for "-classpath"