Make TerminalType a parameter and default to xterm

[Windos]

This addresses issue #6.

I've made TerminalType an optional parameter, which defaults to 'xterm', so that it can be set to whatever the user needs.

Ideally, I'd like to autocomplete a list of valid terminal types... but I wasn't able to find a way to enumerate them. I get the feeling it's the sort of thing that if you're setting it to something other than the default that you probably know what to set it to.

Eventually it'd pay to add a switch to preserve the existing terminal type, it's just a matter of making this user friendly with the parameter sets.