Added event OptionParsed on OptionSet

Added a new event "OptionParsed" on OptionSet that fires whenever one of the options it contains has finished parsing, containing the parsed OptionContext.
If an option is added to an OptionSet, then somehow gets removed from it,
and then added again, OptionSet would register itself twice to the Option's
event.
The other option I had in mind was unregistering the handler in RemoveItem.

On Wed, Sep 24, 2014 at 4:04 PM, Jonathan Pryor <notifications@github.com>
wrote:

> In mcs/class/Mono.Options/Mono.Options/Options.cs:
>
> >  		private void AddImpl (Option option)
> >  		{
> >  			if (option == null)
> >  				throw new ArgumentNullException ("option");
> > +			option.Parsed -= optionParsedEventHandler;
>
> Why would you un-register then re-register for the event?
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/mono/mono/pull/1303/files#r17972626>.
>