Sort order: Use external files for tests

**Warning:** This branch should be rebased and merged ONLY AFTER #110 is reviewed and merged into dev.

This is a small preparation for `*.sass` tests:

- Divide parsing and sorting tests
- Use external files for parsing/sorting tests
- Add tests for correct handling of properties followed by rulesets

Structure of test files is the same as for `vendor-prefix-align`.
I'm lazy to type `utf-8` and name of test directory every time so I added `readFile()` helper.

There are *a lot* of new files, but no scary changes.
Every line is negotiable.

May the force be with you.

![tumblr_lrucb9tp131qczq24o1_500](https://f.cloud.github.com/assets/872004/1566480/a6f52416-508f-11e3-98b7-5e5b6ea7d7f8.gif)