Features missing from the specs

[mbasaglia]

I collected the list of features I think is missing from the specs. Some of these have been discussed to be included in 1.0 version of the specs, we can discuss here whether to include or defer other features

For 1.0 specs:

• gradients
• masks
• track mattes

To discuss:

• more complex shape modifiers
• time remapping
• time stretch
• slots
• blend modes
• split position
• CSS class / ID
• metadata

For later:

• effects
• layer styles
• audio layers
• data layers
• text
• motion blur
• expressions
• 3D stuff