Support the Pan-Nigerian alphabet

[ms-studio]

Add support for the Pan-Nigerian alphabet.

It's a latin alphabet with just a few additional glyphs:
http://en.wikipedia.org/wiki/Pan-Nigerian_alphabet

The idea comes from Edward Trager, who talked about this during LGM'14.

[ms-studio]

The full list of glyphs needed:

• Ɓ / ɓ = (U+0181 and U+0253) (aka uni0181, uni0253)
• Ɗ / ɗ = (U+018A and U+0257)
• Ǝ / ǝ = (U+018E and U+01DD) = DONE
• Ẹ / ẹ = (U+1EB8 and U+1EB9) = DONE
• Ị / ị = DONE
• Ƙ / ƙ = (U+0198 and U+0199)
• Ọ / ọ = DONE
• Ṣ / ṣ = (U+1E62 and U+1E63) = DONE
• Ụ / ụ = DONE

In the latest update, I added Ǝ / ǝ, Ẹ / ẹ, Ị / ị, Ọ / ọ, Ṣ / ṣ, and Ụ / ụ for Regular.

We still need to add them to the Bold version, and create the missing glyphs:

• Ɓ / ɓ = (U+0181 and U+0253) (aka uni0181, uni0253)
• Ɗ / ɗ = (U+018A and U+0257)
• Ƙ / ƙ = (U+0198 and U+0199)