#75 @-moz-document and @keyframes (fix for this issue)

This change fixes #75 and adds two passing test cases for it (`@-moz-document` and `@-[moz|webkit|o]-keyframes`/`@keyframes`).

Furthermore it fixes two glitches (separate commits) which I've stumbled over while implementing this:
   * allow percentage selectors - e.g. `50%: { color: red; }` which can be used for `@keyframes` 
     => see 58926aa
   * leave `360deg` intact (instead of converting it to `0deg`) 
     e.g. needed for: `transform: rotate(0deg);` ...up to... `transform: rotate(360deg)` 
     => see eac38ed

Probably a whole self-contained example (taken from my added test case) is better to convey what I mean:

    ... @keyframes spinnerRotate {
    ...  from {
    ...    -webkit-transform: rotate(0deg);
    ...    -moz-transform: rotate(0deg);
    ...    transform: rotate(0deg);
    ...   }
    ...   75% {
    ...     font-size: 300%;
    ...     margin-left: 25%;
    ...     width: 150%;
    ...   }
    ...  to {
    ...    -webkit-transform: rotate(360deg);
    ...    -moz-transform: rotate(360deg);
    ...    transform: rotate(360deg);
    ...   }
    ... }

Hope you like it!