improve doc, and workaround aliasing detection in MatrixBase_eval snippet (not very nice but I don't know how to do it in a better way)
Renamed "MatrixBase::extract() const" to "MatrixBase::part() const" * Renamed static functions identity, zero, ones, random with an upper case first letter: Identity, Zero, Ones and Random.
map() moves from MatrixBase to Matrix much more documentation/examples/snippets