third party packages again



a few of things to add to the last post:

* The packaging system and packages do not alter your maxima
   setup in any way. They only have an effect during a session in
   which they are loaded, and they don't overwrite any files while
   running. In particular, your startup files are not touched.

* I did not include a way to uninstall the packages.  But it is
   easy to do : in C:\Users\JoeUser\maxima are five files and one
   folder all of which start with `mext'. Simply delete them.

* I encourage upstream authors to give me feedback on the
   packaging.  E.g., I sometimes converted examples to rtests and
   didn't spend too much time getting them to work if they did not
   work immediately. I renamed a couple of functions because I
   don't have a way yet to handle symbol collisions.

* If someone wants to make their own package, examples
   are here
   https://github.com/jlapeyre/mext/tree/master/packages
   A script that makes a template folder for a package is
   here
   https://github.com/jlapeyre/mext/blob/master/bin/make_mext.pl

  -- John