Add makefile targets for doc8 lint, fix formatting/spelling issues

Change-Id: I0f45ffe0ba94fab89f9b38c9b73ed7b9091f1795
diff --git a/docs/requirements.txt b/docs/requirements.txt
index 2fdbc75..cc4662f 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -4,7 +4,7 @@
 livereload~=2.6.1
 nwdiag~=1.0.4
 recommonmark~=0.6.0
-rstcheck~=3.3.1
+doc8~=0.8.0
 seqdiag~=0.9.6
 sphinx-reload~=0.2.0
 sphinx-rtd-theme~=0.4.3
@@ -12,4 +12,4 @@
 sphinxcontrib-blockdiag~=1.5.5
 sphinxcontrib-nwdiag~=0.9.5
 sphinxcontrib-seqdiag~=0.8.5
-sphinxcontrib-openapi~=0.5.0
\ No newline at end of file
+sphinxcontrib-openapi~=0.5.0