Fixed numerous bugs in the string parsing code, including the
one reported in [RT #63918] by Frank Doepper.
[RT #41049] Rewrote literal string parsing to prevent a stack
overflow due to an inefficient regex (reported by Sergei
[RT #91822] Fix compression of GIF images to ensure that output
codes don't exceed 12 bits (reported by Vadim Repin).
The RunLengthDecode filter didn't actually work. Its code has
been rewritten and now passes basic encoding and decoding tests.
Fix Code128 barcode switching from Code C to Code B in certain
cases (reported by Doru Petrescu).