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).