Add .measure functionnality

[ceprio]

Hi, In order to be able to use the simulator.options('AUTOSTOP'), I needed to add the .meas functionality. The code I am pulling is adding the simulator.measure(..) member function to the CircuitSimulation object. As the .meas command takes a lot of different forms, I kept it's parameters as flexible as possible basically taking the type of analysis targeted, it's name and then just a list of strings that forms the command line.

I hope this is to your satisfaction,

Ceprio

[FabriceSalvaire]

Additions:

The .meas(ure) keyword has been added through the simulator.measure(..) member function. This allows the use of simulator.options('AUTOSTOP').
Parallelisation is now more convenient with the use of NgSpiceShared.new_instance() where the management of new instances is now completely automated (temporary dll, instances deletions).