Ignore binary line endings

Immediately after cloning the repo, I had local modifications that wouldn't go away no matter how many times I hard reset or tried checking files out.

```
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	modified:   docs_src/assets/img/bird_blue_32.png
	modified:   docs_src/assets/img/download.png
	modified:   docs_src/assets/img/feature-drag.png
	modified:   docs_src/assets/img/feature-modern.png
	modified:   docs_src/assets/img/feature-module.png
	modified:   docs_src/assets/img/feature-options.png
	modified:   docs_src/assets/img/feature-responsive.png
	modified:   docs_src/assets/img/feature-zombie.png
	modified:   docs_src/assets/img/owl-logo.png
	modified:   docs_src/assets/img/twitter_25.png
	modified:   src/img/owl.video.play.png
	modified:   src/scss/_mixins.scss
	modified:   src/scss/_theme.scss

no changes added to commit (use "git add" and/or "git commit -a")
warning: CRLF will be replaced by LF in docs_src/assets/img/bird_blue_32.png.
The file will have its original line endings in your working directory.
```

After a quick glance at a [GitHub page](https://help.github.com/articles/dealing-with-line-endings) on line endings, I noticed that they set specific file extensions as binary so they would not be modified.

This just follows their example. I also committed the `.scss` files, because it would appear that they did not have the repo-expected LF line endings.