Create macros for simplifying element attribute getters (fixes #1931)
Use getter macros in HTMLImageElement
Stop resorting dictionaries.

Rust is more forgiving about the order of definitions than C++, so there is no
need to try to sort them. Worse, the "sorting" actually causes the order in
the generated file to be non-deterministic.
Use extended attributes to define which interfaces are globals (fixes #1053).

This makes our approach consistent with Gecko's.
Split up macro invocation
Merge pull request #3122 from Ms2ger/globals

Use extended attributes to define which interfaces are globals (fixes #1053); r=Manishearth
Merge pull request #3073 from Manishearth/macro-getters

Create and use attribute getter macros; r=Ms2ger
Merge pull request #3121 from Ms2ger/sorted-dictionaries

Stop resorting dictionaries; r=abinader