Fixed a typo in readme.markdown
Added fix to not take arguments of '0' (zero) as missing
Merge remote-tracking branch 'richardprior/master'
Added test case for required args with value 0
Added .require() as synonym for .demand(), and 'required' attribute for .usage() options - see example/usage-options.js
Added test case for 'alias' option in options object, and corrected examples/usage-options.js
Added .strict() method, to report error if unknown arguments are given
Added .requiresArg() method to specify options that take a mandatory argument value
Update readme