devel/exomizer: Add new port

Exomizer is a cruncher for old 8-bit computers, with focus on the MOS
6502 CPU. It can create self-decrunching executables for a variety of
these systems, as well as plain crunched data. Some decrunching code
for the target systems is bundled.

Approved by: tcberner (mentor)
Differential Revision: https://reviews.freebsd.org/D37965