Specify required modules

The modules that we depend on are not specified in Makefile.PL so checks
are note done when running it. We should change this so that it can
detect if any of them is missing.

Specify the names of the modules used by the program and the minimum
version of them. It will probably work with older versions as well, but
these are the oldest versions that it has been tested with.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>