Not-so-small rewrite

[OPNA2608]

Abit of a rewrite, innit?

(Branch name & comment on first commit is misnomer, I do have plans to finish a buffer backend before cleanup & merge.)

Closes #10. Current set of tools work on 16-bit DOS with this, buffer size could surely use some platform-specific tuning & CMake exposure though.

• [ ] Buffer-based I/O backend
• [ ] Convenience function for FILE-to-FILE I/O, replacing current copy-pasting
• [ ] Cleanup