Crash if certain non-ascii characters in model file.

[emitra17]

bnf_20180824-101129.log

doom_comment.bngl.txt

[wshlavacek]

Fixed in 97917b3. All file open() calls for user input files now specify encoding='utf-8' with errors='replace', so non-ASCII characters in model files, config files, and data files are handled gracefully instead of crashing.