Completeness is wasteful

[simoncozens]

In the common case of using glyphsLib to convert to UFO as part of the fontmake pipeline, all of this code is unnecessary:

    self.to_ufo_background_image(ufo_glyph, layer)
    self.to_ufo_guidelines(ufo_glyph, layer)
    self.to_ufo_glyph_background(ufo_glyph, layer)
    self.to_ufo_annotations(ufo_glyph, layer)

Converting any non-master, non-brace layers is also wasteful.

[khaledhosny]

Not only wasteful, Glyphs files might have some garbage there (e.g. layers with duplicate names) that will not be used for anything but will break the build anyway.

[moyogo]

Color layers can have the same name if they have the same color. #573

[simoncozens]

Incidentally the performance impact of doing less is pretty minimal in the grand scheme of things: https://daltonmaag.github.io/pipeline-perf-tracker/results/

[madig]

Profile of fontmake when compiling Noto Sans to a VF from a .glyphs file:

A lot of time is wasted on 1. writing intermediate UFOs to disk because MutatorMath needs that 2. parsing the file.

[simoncozens]

Use the new parser.