[css3-animations] CSSKeyframeRule.keyText is wrong

The description of the keyText attribute for the CSSKeyframeRule
interface is still wrong.  I believe this issue was raised a long time
ago, but it hasn't been addressed, so I'm repeating to keep it from
being lost.

Right now, it states that the value of keyText is a string containing
the serialization of a float between 0 and 1, corresponding to the
percentage that was originally specified in the keyframe selector.

This is wrong, and also weird.

It's wrong because the keyframe selector can have multiple percentages
- "0%, 50% { color: blue; }" is valid.  So, this needs to be changed
to be a comma-separated list of numbers.

It's weird because it turns the percentage in [0%, 100%] into a float
in [0,1].  We don't have this kind of conversion anywhere else in CSS.
 I don't know if this can be changed at this point, but if it can, it
would be great to keep them as percentages.  (Converting from/to to
0%/100% is still okay.)

~TJ