Create Parallax Propeller backend

[ikskuh]

The Parallax Propeller is a multicore microcontroller with a unique architecture. Having 8 cores, each with 512 general purpose registers make the CPU very different from classic RISC/CISC machine.

Registers can be adressed and used as RAM, each instruction might be conditional.

An ISA description for Propeller 1 can be found at https://www.parallax.com/product/propeller-1-chip-44-pin-qfp-chip/ ("Downloads & Resources" tab), description for Propeller 2 is still work in progress and can be found here: https://www.parallax.com/product/propeller-2-evaluation-board-rev-c/ ("Downloads" tab)