Introduce the memory_base field in the BM file metadata

[redoste]

This makes bm bytecode compiled from bang significantly smaller because the stack is no longer included in the file. Furthermore, debasm looks way cleaner because it doesn't print the stack anymore.

The behavior of native targets remains the same.

[rexim]

@redoste this looks interesting. I'll take a look into it a bit later, sorry. Thank you for the PR!