Rethink of const, assignment and resizing. Introduced a new ResizeArray
that *can* resize. Array can only be assigned once. Introduced Matrix
for the ugly Array in array in array constructs (Removed
FixedSizeMatrix). Removed nil() constants, as you can use a nullptr
instead.
Improved messages
Removed operators that can cause unintended copies (double frees, that
is)
Applied new Array semantics to all code using it. Als added some (but
not enough) tests for Array and consorts.