Derani diphthong reform

When writing Derani, we could get rid of the diphthong mark (◌󱛎◌), and instead reuse more consonant glyphs to write falling diphthongs. This makes the writing system more compact and reduces the amount of marks underneath vowels.

Official	Reform	Mnemonic
󱚺󱛎󱚹 (aı)	󱚶 (  aı / d)	"High" spiral
󱚺󱛎󱛃 (ao)	󱚳 (  ao / p)	󱚺 (a) with a tail
󱚴󱛎󱚹 (eı)	󱚸 (  eı / z)	󱚴 (e) with an 󱚹 (ı) flourish
󱛃󱛎󱚹 (oı)	󱚽 (  oı / nh)	"Low" spiral

Hoemaı called this "probably not a bad idea" so maybe we should start using it!