Call function instead of method in global flag counting.  Allows lib to work in older versions og Go.
Merge pull request #1 from dbmedialab/master

Call function instead of method in global flag counting.
Justify command usage output.
Allow subcommands to define that they require arguments.
Merge pull request #2 from dbmedialab/master

Justify command usage output.
Fix required flags usage message formatting.
Required flags should not be called required args. Fixes #5.
Checks whether required flags are set or not. Fixes #6.
Fixing tests.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	command.go
Reversed changes to the On() method.
Added the 'help' command.

Added the help command which can optionally take over the role of the -h
command for individual commands, freeing up that flag for other uses.
When used without arguments, will display the usage string.  When used
with the name of a command, will display the usage string of that
command.

Also added an prearg override for use with the help command to avoid
requiring a prearg when display command usages.
Added the ability to specify a set of minimum arguments.