Generate a basic documentation website with the mkdocs toolkit.

No content yet other than man pages.  To make the man pages render
nicely in mkdocs, I removed the static %-headers and put the code for
them into default.md.tmp.do instead.  That way, the raw input redo-*.md
files will look right in mkdocs.

Documentation/mkdocs.do

@@ -0,0 +1,9 @@
+redo-ifchange doc.list
+xargs redo-ifchange mkdocs.yml <doc.list
+
+if type mkdocs >/dev/null 2>/dev/null; then
+	mkdocs build
+else
+	echo "Warning: mkdocs is missing; can't generate website." >&2
+	redo-ifcreate /usr/bin/mkdocs
+fi