Add DESTDIR support to install and uninstall targets

Signed-off-by: Pauli Nieminen <suokkos@gmail.com>
Add comments to the makefile

Signed-off-by: Pauli Nieminen <suokkos@gmail.com>
Detect all supported cxx sources

Signed-off-by: Pauli Nieminen <suokkos@gmail.com>