Optional buffered mode

[Atemu]

nom currently passes through all build output to the terminal which can cause flickering and slowdowns (#24, #95). In such cases, it'd be useful to have an optional buffered mode which discards parts of the log output and only updates the output at a fixed maximum rate.

This should probably be off by default as it'd miss some output when lots of things are happening in the output.

Bonus points if this buffered mode could be toggled at runtime via keyboard input.

[maralorn]

Need to figure out how exactly to do this, but I had something like this in mind anyway.