NCrystal python plugin manager

Package providing an ncrystal-pluginmanager command, which searches for dynamic NCrystal plugins (modular shared libraries) installed into module directories of python modules named "ncplugin_*" in plugins/ subdirs.

When an ncrystal-pluginmanager command is available, the NCrystal library itself will use it to get a list of such plugin files to load. This makes it possible to simply install an NCrystal plugin via "pip install ", and then have NCrystal pick it up automatically. This is meant to be easier than the alternative of compiling the plugin code manually, and then appending the resulting shared library to the NCRYSTAL_PLUGIN_LIST environment variable.