Print flag errors while ignoring unknowns
Merge pull request #25 from marksteve/master

Print flag errors while ignoring unknowns (Fixes #24)
Added documentation for the required flag
Fix small indentation issue
Run go fit
Do not show default value in help if it is the zero value
Convert pointer values to string recursively
Updated documentation for optional-value and default tags
Do not parse flags as optional arguments
Added documentation for groups and commands
Make docs on github more concise

Remove the details, which can be found on github.
Added option to stop parsing after first non option

This behavior conforms to strict POSIX behavior,
similar to getopt + or POSIXLY_CORRECT
Added documentation for command execute
Run go fmt
Added documentation on the Command interface
Allow specifying default/optional value tags multiple times

This is allowed to specify multiple values for
maps and slices, as well as multiple arguments
for function calls. For other types of values
the last value will be set.
Added optional doc
Added example with commands
Include toplevel options in alignment calculation

Fixes #22
Wrap command long description