add option to include the line highlights in URLs copied to the clipboard

[bgreenlee]

Thanks. I think it's better if we just turn it on and not bother with a setting, since you can get the URL without line highlights by just not selecting anything. I pushed the fix: https://github.com/bgreenlee/sublime-github/commit/c145ee93a163cbe081f08a05d4eb5e6f80a037d4