Fixes for twine js generation

ezshrequested to merge
ezsh/fc-pregmod:fix-twine-js into pregmod-master

Do not put Twee tag into the file, ignore "art" subfolder, workaround sed script problem with '//' in string literals

Addresses problems of !3385 (merged)

Generated file works fine when pasted into Twine (2.2.1) "Edit Story JavaScript" window.

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