Changing the list of vendor prefixes in gradient mixin

The gradient mixin do not need the ms, because IE uses w3c instead
Remove duplicated hyphen in gradient mixin just after the vendor prefix
Created new transition-transform mixin

Created this mixin in _css3.scss to handle the transitions of transforms
Updating readme.md file

- Create documentation for transition-transform
- Update transform-property example
Add animation mixins

resolves #6
Add unselectable placeholder

Resloves #7
Adding composer.json

This allows luigi to be pulled in using composer
Removing trailing comma in composer.json
Updating composer.json and adding licence

Luigi is now licenced under GPL v2.

Also added composer.json so it can be submitted to packagist. This
resolves #5
Adding bower.json file for installation through there
Addition of spritesmith mixins for use with gulp

Related to #9
Merge branch 'develop'