CLI: change argument naming convention

As in all other Unix/POSIX tools and JVM language compilers, multiple words
comprising the argument name should be lowercase, separated by dashes
CLI: change "-suppress warnings" option to "-nowarn"

Following the rule of the least surprise: this option is named "-nowarn" in
other JVM language compilers. Besides, having an option with an argument which
can take exactly one predefined value is sort of confusing
Minor, move utility method out of an interface
Minor, use a simple MessageCollector in ScriptTest
KDoc: drop "-docOutput" as 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"