Some echo-ed strings in the Makefile contain \r and \c sequence characters. They are not interpreted by default and require the -e flag to be passed to echo. This commit adds it everywhere it is needed for a better and more consistant output during the installation.
Packaging scripts often use the DESTDIR=/some/directory variable to make the build system install the binaries in a specific directory which will be compressed to create the package. This commit adds support for this variable, by introducing a new INSTALL_DIR variable in the Makefile and replacing PREFIX by INSTALL_DIR everywhere it makes sense. Note that by default, INSTALL_DIR=$(PREFIX) so there should not be any compatibility problem with this commit.