Suggestion: rename episodes_length to compute_episodes_length

[RylanSchaeffer]

If I can make a suggestion, perhaps you could rename the function mushroom_rl.utils.dataset.episodes_length() to mushroom_rl.utils.dataset.compute_episodes_length(). This would better match your function naming convention (e.g. compute_J(), compute_metrics()) and would also allow me to name the returned variable episode_lengths.

Thanks in advance!