enforce RAM initializating to all zero

[jan-ferdinand]

In our current design, we can't enforce that the RAM is initialized to all zeros. As discussed with @aszepieniec, the following changes are the least invasive way of achieving this stated goal.

1. Upon encountering (as opposed to executing) either instruction read_mem or write_mem, the processor's registers RAMP and RAMV get updated.
2. In the RAM Table, whenever a new contiguous RAMP region starts, the RAMV is 0. This includes an initial constraint on RAMV being 0.

I'm happy to provide assistance and more details to anyone considering tackling this issue. It's probably best to wait until #139 is done, i.e., #144 is merged.