API guidelines: iterator type names should match the methods that produce them.

[nical]

This is a sub-issue for #44.

We should audit the docs/code of each lyon crate and check that iterator type names match the methods that produce them`.

I know that most of the iterators in lyon crates don't follow this convention.

[nical]

Here is a list of the methods/iterators and the names they should change to:

In lyon_bezier (@anna-liao currently working on it):

• CubicBezierSegment::flattening_iter/CubicFlatteningIter -> CubicBezierSegment::flattened/cubic_bezier::Flattened
• QuadraticBezierSegment::flattening_iter/QudraticFlatteningIter -> QuadraticBezierSegment::flattened/quadratic_bezier::Flattened

In lyon_path:

• PathIter -> Iter

In lyon_path_iterator:

• FlattenginIter -> Flattened (the method name is already flattened)
• PathStateSvgIter -> SvgPathIter (ideally PathIter but conflicts with the other one below).
• PathStateIter -> PathIter
• SvgToPathIter -> PathEvents