Missing support for Coptic script

[stweil]

Training of Tesseract with tesstrain and a text containing ϯ creates a unicharset file which includes this line:

ϯ 3 0,255,0,255,0,0,0,0,0,0 Coptic 273 0 273 ϯ	# ϯ [3ef ]a

lstmtrain complains about a missing file:

Failed to load script unicharset from:data/Coptic.unicharset

[stweil]

See also https://github.com/Shreeshrii/tessdata_coptic.