Support messaging users in irc: and ircs: URL handlers

[mjgardner]

Please support URLs from other apps that include a nickname to message.

Examples:

• irc://example.com/joebloggs,isnick
• irc://example.com/joebloggs,isuser

This format comes from the following documents:

• irc: urls in Mozilla
• Internet-Draft: irc: URL scheme
• Internet-Draft: Uniform Resource Locator Schemes for Internet Relay Chat Entities

More complete support for these URL formats would be nice but can be a separate issue.

Thanks!