Remove support for old browsers

According to the issue: https://github.com/paulirish/css3please/issues/123

Remove:
1. -webkit-border-radius
2. -webkit-gradient, -moz-linear-gradient, -o-linear-gradient
3. -moz-transform, -o-transform
4. -moz-transition, -o-transition
5. -moz-animation, -o-animation, @-moz-keyframes, @-o-keyframes
6. -o-tab-size
 
Leave:
1. -webkit-box-sizing: according http://caniuse.com/#search=box-sizing Safari 5.0 and Android 2.3-3 use -webkit prefix.

Add:
1. Comments about Opera 15+ support to -webkit prefixed properties: -webkit-transform, -webkit-animation.
2. Update comment for -webkit-transition support: Safari 3.2-6 and add Android 2.1+, iOS 3.2-6.1.