test, docs: Add a linter for testing markdown, and fix up our docs

While writing docs, I couldn't remember what the correct style was
supposed to be, and I remember someone complaining about this
previously, so I decided to add a linter! I excluded a bunch of annoying
style rules, but if we find more we can add those to the list too.

Hopefully this gives us a more consistent feel throughout.

misc/make-deps.sh

@@ -94,4 +94,5 @@ go get golang.org/x/tools/cmd/stringer			# for automatic stringer-ing
 go get github.com/tmthrgd/go-bindata/go-bindata	# for compiling in non golang files
 go get github.com/golang/lint/golint			# for `golint`-ing
 go get -u gopkg.in/alecthomas/gometalinter.v1 && mv "$(dirname $(command -v gometalinter.v1))/gometalinter.v1" "$(dirname $(command -v gometalinter.v1))/gometalinter" && gometalinter --install	# bonus
+command -v mdl &>/dev/null || gem install mdl || true	# for linting markdown files
 cd "$XPWD" >/dev/null