more expressive matrix method names
A problem was recently encountered by @philipc while porting some foam-extend code.
In the OpenFOAM Matrix class, we use
m() for rows and
n() for cols, whereas foam-extend use the opposite naming.
This obviously makes for some very difficult error-finding.
Since there is nothing intrinsically meaningful about
n, I suggest that we use
cols() instead (method names as per Eigen3) and mark
n() as deprecated. This would help identify these types of pitfalls in the future.