Adds an opendingux port, tested working on RG300x, but should work on other devices using the same chipset/os. Initial work done by gameblabla. I made a few changes from that initial port (mostly allowing screen stretch to change). I tried to get it building with SDL 2.0, but it was crashing and I'm unsure why, so I stuck with SDL 1.2
[X] This pull request is for a single Feature or BugFix
[X] Your code builds clean without any errors on all platforms
[ ] You have added unit tests (if this is a change to the core Pico 8 emulator)
Adds an opendingux port, tested working on RG300x, but should work on other devices using the same chipset/os. Initial work done by gameblabla. I made a few changes from that initial port (mostly allowing screen stretch to change). I tried to get it building with SDL 2.0, but it was crashing and I'm unsure why, so I stuck with SDL 1.2