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.
Yeah, since that field is guaranteed to be a float it's better not to use pandas. Pandas supports a richer concept of null which comes with a perf hit. I would've used bottleneck functions like `anynan` but `bottleneck` is not a dep.