Add maximum number of steps option

[eftsung]

This will add an option for the maximum number of steps to terminate an epoch early despite having training/evaluation steps left.

Motivation
On slower setups, i.e. underpowered GPUs or CPU mode, an epoch could take a particularly long time to complete. Often for benchmarking purposes, there's no need to run this to completion, as a smaller number of steps is all that is needed for these slower setups.