Linux support for Enhanced Steam Standalone

Hi jshackles

I read in various places that it should be possible to make Enhanced Steam Standalone work on Linux and Mac OSX, so I decided to try. After figuring out how your existing setup worked, I wrote a bash script which does essentially the same thing as start-stop.bat. I wrote the script from scratch, but I modeled it closely on your script.
Once I'd gotten it working, I edited README.md with instructions on using it.

I hope this is useful,

MageJohn