refactor completion into Parser.ParseArgs
call p.printError only once
test required options
test an entire completion structure
completion should not implement the Commander interface
remove "__complete" command invocation
Merge pull request #84 from zimmski/fix-required-flag-completion

fix required flag completion
Implement verbose completion

Add tests for verbose completion and document it
do quoting in INI and help
do not inline printOption and rename it to writeOption
handle empty slices/maps directly
refactor commentOption and writeOption
Option.iniUsedName was never used
do not loose read in quotes
always check if default values need quotes
quote tabs too