Add description for show help and dynamic function

[RaminNietzsche]

No description provided.

[skeeto]

I'm not really interested in making such a substantial change to the API. The intent is specifically for each argument to be processed in its own switch case without any special callbacks or automatic handling by Optparse. Callbacks are particularly less useful for this purpose in C since they aren't closures and cannot modify variables local to the function initiating the process.