`--minimum-ram-size` option is not respected

[ZhekaS]

The --minimum-ram-size option seem to not do anything. It is associated with the minimum_stack_size variable for some reason, which is not being used further in the code. https://github.com/tock/elf2tab/blob/06b05fdad764c59c279a50686ccd512f544fb824/src/cmdline.rs#L64-L72

[bradjc]

This is (obviously) an issue. I'm guessing this stems from changes in how elf2tab decides on how much memory to tell the kernel the app needs.

There might be backwards compatibility concerns, but actually documenting how elf2tab computes the memory an app needs, and what flags do what, would be worthwhile.