doc: massive refactor and simplification to migrate to mkdocs

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

doc/config/Makefile.am

@@ -0,0 +1,7 @@
+configdocsdir   := @docdir@/doc/config
+configdocs_DATA  = README.md cgroups.md env.md files.md index.md	\
+		   limitations.md logging.md rescue.md runlevels.md	\
+		   runparts.md service-env.md service-opts.md		\
+		   service-sync.md service-wrappers.md services.md	\
+		   sysv.md task-and-run.md templating.md tty.md
+EXTRA_DIST = $(configdocs_DATA)