Request: Support for Akan/Twi, Lingala, Dinka, Manding and Ewe

This is mostly a continuation of my African language requests. The orthographies of these languages all share the letters ɛ ɔ to represent half-open vowels similar to the ones in English ‘share’ and ‘law’.

Akan (~9.3 million speakers) and Lingala (~9.1 million speakers) only use those extended letters. Tone can be marked with combining diacritics (at least ɛ̀ ɛ̀ ɛ̂ ɛ̌), but they’re rarely used outside of dictionaries.

Dinka (~1.3 million speakers) uses the letters ɣ ŋ in addition to ɛ ɔ, as well as the combining diaeresis to represent a series of breathy vowels.

The Manding languages (at least ~8.8 million native speakers) use the additional letters ɛ ɔ ŋ ɲ when written in Latin script. The vowels can take the same set of tone marks as in Lingala, but they’re only used in dictionaries.

Ewe (~3.6 million speakers) has the largest character set in this request. Besides the previously mentioned ɛ ɔ ɣ ŋ, it also uses ɖ ƒ ʋ, as well as combining tone marks. Note that ƒ is an actual letter in Ewe, not just the florin sign (see issue [#42](https://github.com/adobe-fonts/source-sans-pro/issues/42) on the Source Sans repository).

The issue names no source files, tests, or entry points. Start by locating the font sources and build instructions in the Source Serif repository, then verify completion by checking coverage for the requested Akan/Twi, Lingala, Dinka, Manding, and Ewe letters and combining marks across the relevant font outputs.

索引モデルが issue の本文から書いたものです。