Propagete method return types.
Remove old VM_IS_CLASS marker.
Adds some tracing events.
Reworks the way iterators work.

Still not very happy with it but better than the way it was before. For vectors, iteration is now about 10x faster and doesn't allocate memory.
Compiler bug fix related to coercing class constructors.
Stub apply filter.
Adds option to disable image conversion and uploading.

This is useful when trying to get a more accurate execution profile.
Adds a larger stage scale factor.
Merge branch 'nat' of https://github.com/mozilla/shumway into nat