Extract Option classes from cli.toit into options_.toit

cli.toit had grown to ~1856 lines. Move all Option-related classes
(Option, OptionString, OptionEnum, OptionInt, OptionPatterns, OptionPath,
OptionInFile, OptionOutFile, OptionUuid, Flag, InFile, OutFile,
CompletionCandidate, CompletionContext) into a new options_.toit file
and re-export them from cli.toit.

Author: floitsch