conf: Generate and install config sippets for option descriptions

The strongswan.d directory is also created relative to the configured
location of strongswan.conf.

conf/plugins/test.opt

@@ -0,0 +1,30 @@
+charon.plugins.test.opt
+	This is a normal option without default
+
+charon.plugins.test.noncomment := set this
+	This will not be commented out
+
+charon.plugins.test.def = default
+	Option with default
+
+charon.plugins.test.sectionnocomment.opt = val
+	The section this is in has no description
+
+charon.plugins.test.sub {}
+	This section has comments
+
+charon.plugins.test.sub.opt = option in sub
+	Section option
+
+charon.plugins.test.<commented> { # }
+	Commented example section
+
+charon.plugins.test.<commented>.val = value
+	This is commented anyway
+
+charon.plugins.test.<commented>.assign := value
+	This is commented too because of the commented section
+
+charon.plugins.test.sub = value
+	Sections can also be options with values
+	Longer description with **bold** and _italic_.