[#84]Export Speed Up

Exporting a character with 15k polys now takes 5-10 seconds as opposed
to 10-20 minutes.
It's quite mysterious because:
1. You are iterating over all `face.edges` but `use_sharp_edges` and `has_sharp_edges` variables will be set based only on the last one.
2. You are iterating over `face.edges` inside `for vert in face.verts` but `verts` are not used in this loop.