Use "true" argument in calls to cholesky methods.
Improve Doxygen documentation, add at() methods and value assignment operator.
Remove const at() methods (swig does not recognized them)
Correct invert() method.

The invert() method does not need to call the Cholesky decomposition, as cholseky_invert() does this itself.
Add missing line continuation marker.
Improve Doxygen documentation, add at() method and value assignment method.
Adapt to new matrix interface.
Use at() method for argument range checking test.

The [] access operator does not provide range checking anymore, hence the at() method has not to be used for range checking.
Add value assignment operator check.
Expose GTools functions to Python.
Replace operator* by __mul__ operators.
Add matrix handling howto.
Complete Doxygen documentation.
Include information about matrix class reworking.
Rework matrix transformation methods.

The methods transpose(), invert() and abs() now return a matrix instead of working on the actual matrix. The transpose(), inverse(), abs(), and negate() friend functions have been removed. The method solve() has been added that solves the linear matrix equation.

The Cholesky methods now also return a matrix instead of working on the actual object.
Adapt to new matrix transpose(), invert() and abs() methods.
Add solve() method.