Feature parity between syntaxes

[futursolo]

This issue aims to investigate feature parity between macros. So both macros flavours have a consistent behaviour.

Feature missing on one side needs to be introduced on the other flavour.

This also ensures that features are implemented properly.

Differences:

• [x] literal does not support @media and @supports in Block
• [ ] literal does not support interpolation on keys of style attributes
• [x] inline does not support arbitrary at-rules (not a whole lot can be done here. Can be managed in #29.)