[Proposal] Add color names

[robert-ancell]

A renderer might want to use one TVG file to render multiple similar images that differ by an accent color. To allow this I propose adding optional names to the color table. Suggested format:

Header:

...
color_count VarUInt
color_name_count VarUInt

Color Name:

color_index VarUInt
name_length VarUInt
name [name_length]u8

• Names may only use the characters a-zA-Z_.
• A color may have multiple names
• If a name is used multiple times only the first entry is considered valid.

[robert-ancell]

Alternatives considered:

• Just use the indexes instead of names - this is likely to break if a file changes color order or doesn't support this feature.
• Have a list of names that match the order of the colors - doesn't allow multiple names

[ikskuh]

I don't think this is a feature that suits TinyVG well, as it already is an application specific thing, and you can then also just use a well-defined index instead of a name, making the tooling such that it preserves well-defined indices. Remind yourself that you could also just implement a custom color encoding and use names instead of RGBA values directly