Warn if glyph name too long

[simoncozens]

According to the post table spec,

Names must be no longer than 63 characters; some older implementations may assume a length limit of 31 characters.

This implements a check for name length of glyph names in the post table. As glyph names are purely informational, I have made this a warning rather than an error.

[ctrlcctrlv]

Thanks Simon! Yeah, this will break poorly implemented software, like FontForge. (Cf. fontforge/fontforge#4751.) I imagine other similarly badly-thought-out C code is just doing char[63] somewhere.

[khaledhosny]

We either should truncate the names (tricky as it can result in duplicate names) or drop the names entirely and change the table version to 3 (should be safe on the web), if we really think this is potentially an issue. Warnings are good, but OTS main job is a sanitizer not a linting tool.