add pip support and some docs

filter_plugins/packages_filters.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python3
+class FilterModule(object):
+	def filters(self):
+		return {
+				'packages_by_provider': self.packages_by_provider
+			}
+
+	def packages_by_provider(self, packages, provider, defaults=False):
+		filtered_packages = []
+		for key, value in packages.items():
+			if value == None:
+				continue
+			if defaults:
+				package = dict(defaults)
+				package.update(dict(value))
+			else:
+				package = dict(value)
+			if package['provider'] == provider:
+				filtered_packages.append(key)
+		return filtered_packages