Dev numba

[dlohmeier]

I would like to suggest some changes to the pipeflow procedure:

• All derivatives (for now only implemented in hydraulic calculations) are calculated globally, i.e. the branch component's calculate_derivatives_hydraulic is moved outside that class, as this behaviour is always the same.
• It is possible to define your own additional procedures for updating the pit before and after derivative calculation. This is helpful for instance in case of pressure lift recalculation or for branch components whose pressure difference does not depend on the flow.
• I implemented some parts in numba which should accelerate the pipeflow calculation in most cases.

Numba does have downsides that should be discussed:

• It is very hard to debug numba code.
• Compilation takes time, which leads to the fact that in case of just one pipeflow for a small network, this solution is even slower. This can be seen from the test timing, which will be slower with the numba implementations. The larger the dataset and the more times the function is called, the larger the benefit.
• It might be more difficult to guarantee a smooth run on all types of machines (although the numba developers really try to make it work anywhere).

[dlohmeier]

This is also a suggestion to handle issue #199.

[dlohmeier]

I will create a new branch for further development.