Added filter: alpha in .opacity for ie browsers
Better support for css3 transitions

This PR integrates the set of mixins regarding css3 transitions with: 
 - "transition-property"
 - "transition-timing-function" (abbreviated to transition-timing)
 - "transition-delay"

Example:

a {  
  .transition-property(color);
  .transition-duration(.3s);
  .transition-timing(ease-in);
}
Add .horizontal-gradient mixin
Update elements.less > border-raidus

The first argument should be @top-left, as well as the order of the original arguments of border-radius.
Merge branch 'issue49'
added gitignore
Merge branch 'issue46'
Merge branch 'issue16'

Conflicts:
	elements.less