Add support for flags of type string. Should fix jingweno/gotask#10
Remove commented line
Fix string flag rendering in the help message
Add support for default value in string flag
Fix variadic in Error/Errorf
Swap test expectations to make sure order doesn't matter
Some space
First attempt at supporting string flag
Remove Println used for debugging
Fix man_page_test
Distinguish between mandatory string flag and string flag with default value
Fix String flag comment
Add doc