Numerical solution of algebraic equations implemented for S-function target.

Equation solving requires the Matlab Optimization Toolbox to be installed.

Code has been changed from C++ to C to allow mex files to be built with LCC,
the compiler bundled with Matlab.

Parameters are now obtained from numpar.c instead of a dialogue box.

`mtt <sys> sfun zip` creates all necessary files for building the model mex files.