Argument processing improvements

Utilising new functionality from PHP.Gt/Cli upstream, arguments on commands can now be nullable, which has the major improvement of not having to pass arguments with no value at the end of the argument list.

Terminology has been changed in this release to introduce --watch and --now. The watch argument continues the cron execution forever (similar to how PHP.Gt/Build works), and the now argument runs all cron tasks at the start of the execution, which is very useful when developing locally.