xolotl should support standalone integration

[sg-s]

See HDF5 API for C++

• [ ] g++ should compile a standalone binary
• [ ] should write a wrapper function that is multithreaded, to run N-1 threads
• [ ] each thread reads a .mat file with some integration parameters, using the HDF5 library
• [ ] each thread should write out V, Ca (and maybe other things) to a .mat file (using the HDF5 library)

advantages over xgrid:

• will not need MATLAB's parallel processing toolbox
• should be much lighter on memory, since we're using multithreading, not multiprocessing
• allows for MATLAB-less computation, since standalone binary can work on its own

Steps to be done:

• [ ] write a function that writes out state to disk in a binary format (see this)
• [ ] write some C++ code that can read out written states from disk (see this)
• [ ] write a new version of mexTemplate that can uses a different entry point
• [ ] write a fake version of mex.h that provides some basic functionality for compatibility
• [ ] write a new version of transpile