4489_byteloader
* load any number of bytes
* from any disk position
* on any connected drive
* to any memory address
* small
* portable
* self-contained
* verifies checksums
* no deadlocks
* retries on timeouts
* retries on errors
* returns errorcode if max_retries exceeded (default: 8)
* does not interfere with existing interrupt, cia timer, blitter or copper use
* respects official hw docs and bulletins
* compatible with iffy /rdy drives
* tested on A500, A500+, A600, A1200/020, A4000/040
* updates, issues, improvements: https://github.com/4489