Add interface to an LPN solver to define BCs

[ktbolt]

The solver currently uses the General Boundary Conditions (GenBC) framework to define custom inlet and outlet boundary conditions for a simulation using a lumped parameter network (LPN).

The GenBC framework is implemented as an external executable Fortran program called by the SimVascular flow solver svSolver. The executable is called by svSolver during execution to provide values for custom boundary conditions. The GenBC framework has a couple of disadvantages

• The LPN must be coded in Fortran
• It is extremely slow to execute an external program and read its results from a file

A better solution is to create an interface to an LPN solver that can load the LPN solver as a shared library and directly call its functions to return the BC values at a given time step.

[ktbolt]

I've modified the C++ svZeroDSolver code to build a shared library that can be loaded programatically. https://github.com/ktbolt/svZeroDSolver/tree/convert_cpp.

I've added a test for calling the LPN interface from Fortran. https://github.com/ktbolt/cardiovascular/tree/master/lpn-solver-interface/fortran