fix uri escaping

Hi, with the current gem I have no way of sending to channels with / in the channel name. This should be valid according to the docs but it's not, and instead seems to generate invalid requests.

I am using http://rack.rubyforge.org/doc/Rack/Utils.html#method-c-escape_path instead of URI escape, as that properly escapes uri components.

URI.escape does not seem to escape + either, or =, and it is possible that sending to a channel name with + instead will confuse the + with a space