Log Message:
lang/forth-retro: import forth-retro-12.0.2018.1

RETRO is a clean, elegant, and pragmatic dialect of Forth. It provides
a simple alternative for those willing to make a break from legacy
systems.

The language draws influences from many sources including traditional
Forth systems, cmForth, colorForth, Factor, and Parable. It was
designed to be easy to grasp and adapt to specific uses.

The basic language is very portable. It runs on a tiny virtual
machine (Nga), which is written in C. There are multiple interface
options, the main one (rre) is buildable with just the standard C
compiler and libraries on most systems.