Allow users to disable quoting completely or use a different quote string

Allow users to disable quoting completely or use a different quote string.

This is needed to fix `grunt-contrib-sass` as the current issue there is only solvable by removing quoting completely. Otherwise it will fail under Linux and OSX.
Hmm, yeah, good point. That's probably handled as one value: `"--unicorn2=foo bar"`.

// @radkodinev might now even need quoting.