WIP: General perf enhancements

This is mainly targeted at minutely backtests with daily emissions. Having a 1-to-1 emission causes the perf tracking to dominate performance, which I haven't touched. 

Can someone else run this and let me know the timings? Especially with an algo that's public and that I can also run.
I think this might be clearer as `np.all(pd.notnull(vals))`, though this looks like it's a fair amount faster.