Switched from doc8 to rstcheck

rstcheck supports sphinx-specific directives such as linenos

Change-Id: Ica1f6e17fef867eeef056546e7c4bdba51a2079e
diff --git a/Makefile b/Makefile
index 0da130b..4d57f91 100644
--- a/Makefile
+++ b/Makefile
@@ -38,7 +38,7 @@
 rst-lint: doc_venv
 	source ./doc_venv/bin/activate ;\
 	set -u ;\
-	doc8 --ignore-path doc_venv --ignore-path _build --max-line-length 160 $(SOURCEDIR)
+	rstcheck -r $$(find . -name \*.rst ! -path "*doc_venv*")
 
 # clean up
 clean: