relax requirements for orthography abbreviations

[dwhieb]

Orthography abbreviations (such as those used as keys in Transcription objects) should have their requirements relaxed, probably to allow for any ASCII characters.

This will allow users to use whole language/writing system codes if they wish, or more project-specific codes like those for Nisinoon: C-I:1, C-I:2, C-I:Standard, C-I:Revised, C-M:1, C-N:1, C-N:2, C-NE:1, C-NE:2, and similar.