Warn and skip on unsupported .gitattributes pattern syntax Detect negation (`\!pattern`), escape (`\\`), quoting (`"`), and character class (`[...]`) syntax in parse_pattern and skip the pattern with a Logs.warn rather than compiling to a regex that silently matches no files. Change parse_pattern to return a t option to reflect this. Split the README "not supported" list: syntactic cases are warned-and- skipped uniformly, while case-insensitivity and subdirectory .gitattributes are documented as separate limitations. Signed-off-by: Josh Berdine <josh@berdine.net>