Added bridging functionallity to PHP.

[kalaspuffar]

This PR will add a couple of functions to the code so you can add this library as a PHP module and run it directly from the PHP code. I've seen that other glue codes have separate repositories, so this might not be how to implement this. I am still very early in my Rust journey, so I've not looked into multi-repository solutions.

I also did a small bug fix so the library doesn't have the name liblibmathcat.so

Best regards
Daniel

[NSoiffer]

Apologies for not seeing this earlier.

The way I have been dealing with language bindings is to have a separate repo (e.g, MathCATForC, MathCATForPython) that has wrappers for that language. The idea was not to "burden" the main library with these bindings. I don't think the current setup of using separate repos is a good idea and welcome suggestions for how to manage this better.

Two ideas that have come up:

• Make use of Cargo Workspaces
• Make use of github submodules

If you have any thoughts on either approach or another approach, I'd appreciate your feedback. I have heard from some people that I should avoid github submodules.

Also see #193 for another approach to language bindings.