The unit test was so weak that this parenthesis error wasn't spotted
until now. Updated the unit test to don't accept the previous code and
also floats everywhere instead of ints.
Removed functions at(), set() and add(), everything (and more) can be
now done using operator[]. Accessing matrix elements is now done through
column vectors, e.g.:
Matrix4 a;
a.at(row, col); // before
a[col][row]; // now
Note that because operator[] on Matrix returns column vector (there is
nothing like row vector), the parameter "order" is now swapped.
All HTML code and Doxygen shortcuts such as @c, @b and @em are now
rewritten using Markdown syntax, which makes it more readable.
Also updated Doxyfile. Doxygen 1.8 at least is required to generate
the documentation now.