Support 32-bit targets

[0f-0b]

Is your feature request related to a problem? Please describe.

I would like to run the interpreter in a 32-bit environment but met with a panic because it attempts to allocate too much memory.

thread 'main' panicked at …/src/hvm.rs:411:45:
called `Result::unwrap()` on an `Err` value: LayoutError

Describe the solution you'd like

Provide some way to adjust the amount of memory the interpreter allocates.

Describe alternatives you've considered

Switch to 64-bit.

Additional context

A 32-bit environment can be emulated with Miri.

MIRIFLAGS=-Zmiri-disable-isolation cargo miri run --target armv7-unknown-linux-gnueabihf -- run <(echo '@main = 42')