Simple namespaced plugin facility (common documentation)

 straight.plugin is a Python plugin loader inspired by twisted.plugin
 with two important distinctions:
 .
 - Fewer dependencies
 - Python 3 compatible
 .
 The system is used to allow multiple Python packages to provide
 plugins within a namespace package, where other packages will locate
 and utilize. The plugins themselves are modules in a namespace
 package where the namespace identifies the plugins in it for some
 particular purpose or intent.
 .
 This is the common documentation package.