Fix process blocking

Populations don't block eachother, which gives a large speedup especially for large numbers of populations. This was fixed by using RemoteChannel() in Julia.

Some populations happen to take longer than others - perhaps they have very complex equations - and can therefore block others that have finished early. This lets the processor work on the next population to be finished.

Scoring with Pareto Front

Uses equation from Cranmer et al. (2020) https://arxiv.org/abs/2006.11287 to score equations, and prints this alongside MSE. This makes symbolic regression more robust to noise.

v0.2

v0.2 - Add many more operators; increase efficiency