Improves speed of entropy scan

Add signature for bix firmware file format

moved entropy legend

Adding power support

Update deps.sh for Python 3 jefferson

This is used by Zyxel for the firmware in their GS1900 series switches,
but also shows up in Cisco 220 series.

It's really just the U-Boot header with a different initial magic value.

Also minor cleanup in the U-Boot signature.

Jefferson has moved to Python 3. This requires changes to `deps.sh`

Fixed bug in processing internal extractors; if extractor raises an exception, explicitly mark it as failed.

Improved speed of entropy scan by using a list rather than a dictionary for seen values
vastly improved speed with optional numpy/numba implementation

Add signature for Ubiquiti firmware additional data

Update deps.sh

Added Toshiba SSD Firmware Update magic.

add UNIQUE_PATH_DELIMITER to mount command

Added lz4 and zstd comporessions to squashfs.

Improve help output for --dd

travis: Update Python versions

Stop testing on unsupported Python 3.3

Drop Python 3.3 which isn't available anymore, add python 3.7 and 3.8 instead.

Make it clear that ext/cmd are optional and that the type can be a regular
expression.

Newest squashfs in upstream has supported LZ4 (5) and ZSTD
(6) as compression algorithms. However, they didn't exist in binwalk's
current magic library. This commit added the magic values so that squashfs images
compressed by these algorithms could be successfully identified.

Ref:
https://github.com/torvalds/linux/blob/master/fs/squashfs/squashfs_fs.h
https://github.com/file/file/blob/master/magic/Magdir/filesystems

Add signature/decryption support for PGP RSA encrypted session key