Add API v2 support

This request allows us to use HipChat API v2 by adding an command-line and curl options.

Please give me feedback if you have. Thanks!
How about "v"? (A means "A"PI version in this case.)

> Also I don't think it's wise to change the default version to v2 quite yet as people may have automated tools pulling this script down which would then cause their notifications to break.

I see. Your idea is reasonable. Fixed.