Hg fix release script

The release scrip should take exactly two arguments. I also rewrote the error message, personally I prefer a program just to print its usage if it's used incorrectly.
Also I'd like to be told that I could use 'major', 'minor' or 'patch' in in place of the version number... because I was too lazy to read mversion docs so didn't know those arguments existed.

I think the format is be something like <version number | major | minor | patch>