PRHS into a readable class

[willGraham01]

Moving towards #63 |

The argument prhs to execute_simulation is rather unintuitive, being a hangover from when mexfunction was used. With regards to moving towards #70, and making the codebase a bit more readable, this object is broken out into a new class InputMatrices. This class steals some of the functionality of openandorder, and is designed to make the "unpacking" part of iterator.cpp more readable.

In theory, we can also do away with the intermediate variables that are defined in iterator.cpp and work directly with prhs now (although that is not recommended for readability purposes).

• Constant increments of an input_counter++ are no longer needed when unpacking the input matrices - they can be accessed by passing in their names.
• Validation that the input arrays are of the correct type/shape are performed when they are read in by the InputMatrices class, rather than at the start of execute_simulation. This avoids potentially redundant setup/memory allocation.
• The constants like omega, Nt, etc stored in SimulationParameters are now set by calling the unpack_from_input_matrices method, rather than being done directly inside execute_simulation, reducing the code bloat.
• A number of fprintfs -> spdlog::info in line with Use the new logging #87.
• General Docstring tidy up in files that are touched by this PR.

[samcunliffe]

Ah, this is likely going to clash with my refactoring/reworking. (You weren't to know because I didn't tell you or push to my draft PR).

I went for std::vector<std::string> (which could be defined as const and live in a namespace). My reasoning: a vector knows its own size_t and one can do much nicer-looking loops like:

for (auto matrixname : matrixnames) {
     file.read(matrixname);
}

[samcunliffe]

Come to think of it, the matrices in our input and output files define our file type. So perhaps a tdms::File is a HDF5 of this format.

[samcunliffe]

Looks all good!
When you're happy to merge, could you reject #207 at the same time, please?