Clean a BibTeX file by removing text outside BibTeX entries.
Remove each non-empty line that is not in a BibTeX entry, except retain any line that starts with "%".
Arguments are the names of the original files. Cleaned copies of those files are written in the current directory. Therefore, this should be run in a different directory from where the argument files are. If an argument file is in the current directory, the program writes a diagnostic and exits rather than overwriting the file.
A file whose name ends with .gz is read and written compressed.