Log Message:
misc: Add pixd.

pixd is a tool for visualizing binary data using a colour palette. It is in
a lot of ways akin to a hexdump tool, except using coloured squares to
represent each octet.

pixd uses 24-bit color SGR escape sequences.  For a list of terminal emulators
with support for these, see XVilka's list of supporting terminal emulators:
https://gist.github.com/XVilka/8346728