Suggested to delete as handled by auto-prefixing

Most people use auto prefixes so suggested we remove this mixin.
Deleted as handled by native Sass now.
Created _hover.scss

Created a simple mixin to include hover, focus, active states for quicker short hand when writing code.
Update _hover.scss
Delete _hover.scss
Create _hover.scss
Removed _hover from this PR
Merge pull request #19 from terryupton/master

Suggested to delete as handled by auto-prefixing. Thanks Terry.