Calculate checksum of program in memory and compare to expected

Use this to detect tampering by reverse engineers. Honestly not even sure if this is possible.

Write this in C and aim for ~cross-platform compatibility~ a working PoC.

- https://stackoverflow.com/questions/14103061/c-code-that-checksums-itself-in-ram
- https://scholarworks.sjsu.edu/cgi/viewcontent.cgi?article=1180&context=etd_projects
- https://github.com/Barro/self-checksum