Add dynamic module test and helper script

Add dynamic module test and helper script

Add 'modhelp.py' script (python2) to automate module testing and
module generation.

To build and test all modules in the modules/ dir
  $ ./modhelp.py test

To generate a module from template code (good starting point)
  $ ./modhelp init mynewtestmodule

See the script -h option for more documentation.

* modules/modhelp.py: New module helper script.
* modules/mod-test/Makefile: New file. Makefile for the test module.
* modules/mod-test/mod-test.c: New file. Test module source file.
* modules/mod-test/test.el: New file. ert test suite for the test module.
* modules/.gitignore: New file. Local .gitignore file.

Co-authored-by: Philipp Stephani <phst@google.com>