#3 exchange inputting

[Aaron Conole]

I've been using TnT for quite some time now, and would like to see a feature to specify the exchange to
connect to when connecting to a chatroom. I've done some grokking of the toc.el and other .el files, and I
can specify the exchange manually, but a prompt for the exchange number would be great. I don't have
much emacs programming experience, so I couldn't write an input request on my own, otherwise I'd have
written it myself. keep up the great work.