andr1976/HydDown: Alpha

First version working reasonably well with most needed features implemeting. Some work is required to provide meaningful messages to errors in input/yaml. Some convienece features are also lacking such as result arrays stored as pandas dataframe, optimisation/solvers for valve sizing is also lacking. More elaboration on heat transfer correlations is required as well as a transient 1-D heat transfer model to handle other materials than fairly dense metals.