Add suport for // multiline comments

[mathiasschopmans]

Sass seems to support multiline comments escaped by // + indentation
sass/sass#338 (comment)

//
  I will not be rendered
  .box
    background: $gray-dark
    p
      margin: 0 0 5px

Github syntax-highlighting might be also broken, but maybe they're using your package. 😛

This is what it currently looks like in Sublime Text 3.0

Thank your for your investigation!

[JGJP]

This also applies to the use of /* but with the problem that it thinks the multiline comment is going on forever