Memory and variable modification

[dylandreimerink]

This issue proposes to add commands with which the contents of registers and memory can be updated. The purpose of this feature is to explore conditions which normally don't occur or are difficult to recreate while in a debugging session. For example if you want to explore an error case, you can break just before evaluating something and change the value of R1 to trigger an artificial error.

The MVP version of the feature is to have it just work on registers, but being able to change local/global variables would be nice, completely or specific struct members. Additionally to also modify memory we don't have variables for like changing bytes as specific memory locations to change a packet for example.