Unify format of external glyph names files across AFDKO tools

[skef]

A number of tools allow a list of glyphs to be specified in a file as opposed to the command line. These files work somewhat differently for different tools. We should unify the format. We should also consider whether tools not currently supporting such a file, or supporting it only in some situations, should have expanded support.

Some ideas:

• Both comma-separation (on one line) and newline separation should probably work
• The otfautohint version of the file supports ranges, where you specify the first and last element of the range and it fills in the middle. Unlike the other tools it allows the first and last element to be specified by name (rather than GID or CID). This seems useful but it may also go against intuitions about how name ranges work.