Log Message:
py-fonttools: updated to 3.21.0

3.21.0:
[cmap] when compiling format6 subtable, don't assume gid0 is always called '.notdef'.
[ot] Allow decompiling fonts with bad Coverage format number.
Change FontTools licence to MIT.
[post] Prune extra names already in standard Mac set.
[subset] Delete empty SubrsIndex after subsetting.
[varLib] Don't share points in cvar by default, as it currently fails on some \ 
browsers.
[afmLib] Make poor old afmLib work on python3.