Use single-line comments for shared file headings

Changed multi-line comments to single-line comments to hide comments from generated CSS.
Multi-line comments for pattern file headings

Use multi-line comments for pattern file headings, so they are included in the generated CSS
Add blank line between mixin and comments

For the sake of uniformity, add a blank line between mixins and comments
Merge pull request #54 from jessedobbelaere/single-line-comments

Use single-line comments for shared file headings