allow all SSH_KEYWORDS parameters, fix for "yes"

[gjmurakami]

Thanks for doing this. I needed other keywords than what you use.

The fix for 'yes' is a hack, but I hope that you get the idea of what is desired, and you are welcome to do something better.

[gaqzi]

Hm… I started working on making a script that parsed the man page and gave the correct expectations for all the values in the ssh_config file. I would much rather bring that into the library proper.

I'll see what I can do about it this week and hopefully be able to get something with all the options out by the end of the week :)