Rich error reporting + io.js support

before:

unbound variable $undefined-variable in stdin:7386:29

now:

File:../../blocks-touch/tune/tune.scss:29
Message: unbound variable $undefined-variable
Context:
        opacity: 0;
        position: fixed;
        right: 0;
        top: 0;
        transition: opacity $transition-delayasd * 2 $transition-fn;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    }

    &_visible_yes,
    &_visible_no {
        position: fixed;