Introduce module file

Linux/Unix multi-user systems can make use of the module system to load/unload environment configurations for potentially conflicting software packages. Openmpi uses this system on fedora to let you quickly switch between compiler configs without having to keep openmpi enabled for every user on the system.

the davitpy module file is meant to make it possible to provide installable davitpy packages on multiusers systems without interfering with old rst/idl configurations until the davitpy module is explcitly loaded by a user into the user's environment.

The initial content of the file is just a place holder right now.  I want to integrate the specific paths listed in the file into the install procedure so the install procedure generates the correct info for the systemwide deployment of a davitpy package.