Polyfile

Major, partially breaking release. Switches from the TRiD database to using libmagic.

This achieves both a significant speedup as well as drastically reduces false positives.

The --try-all-offsets/-a option is temporarily removed. Also, files are now tagged by their MIME type rather than their TRiD definition name.

Switches to the official KaitaiStruct compiler.
Includes support for parsing the entire [KaitaiStruct format library](https://github.com/kaitai-io/kaitai_struct_formats).

Enhancements to recursive submatching of PDF streams.

Better support for chained PDF stream filters.

Submatch messages are now logged at level DEBUG rather than INFO.

Bug Fixes
* Support custom implementations of `sys.stderr` for logging
* Recursively match against PDF object stream contents

Enhancements
* Gracefully handle SIGTERM and SIGINT
* Output incremental results on early termination
* New `--require-match` option
* New `--max-matches` option
* Can match against filetypes specified with wildcards

Adds `polymerge`, a utility to merge the output of PolyFile and [PolyTracker](https://github.com/trailofbits/polytracker).

Fixes a bug that might prevent files containing JPEGs from being processed properly.