💝 Allow error handlers to access the Cobra' command object (#4)

Allow error handlers to access the Cobra' command object

🎁 Custom error handler (#3)

* Custom error handler

* Call error handler only if the error occurs

💝 A general purpose WithCommand option. (#2)

A general purpose WithCommand option.

Commandline package initial code (#1)

Signed-off-by: Krzysztof Suszyński <krzysztof.suszynski@wavesoftware.pl>