Add support for non-monotoneous in x curves for the profiles

[dov]

Currently the profiling requires (implicitly) that the profiling curves are monotone in x. This should be extended so that non-x monotone curves are allowed as well. This can always be done by splitting a non-x monotone curve into multiple x monotone curves.

Use case: Let's say we want to embed an emitting light with a circular cross section the periphery of the font. Currently this can not be done.