test: Add a check for too long or badly reflowed docstrings

This ensures that docstring comments are wrapped to 80 chars. ffrank
seemed to be making this mistake far too often, and it's a silly thing
to look for manually. As it turns out, I've made it too, as have many
others. Now we have a test that checks for most cases. There are still a
few stray cases that aren't checked automatically, but this can be
improved upon if someone is motivated to do so.

Before anyone complains about the 80 character limit: this only checks
docstring comments, not source code length or inline source code
comments. There's no excuse for having docstrings that are badly
reflowed or over 80 chars, particularly if you have an automated test.

lang/funcs/engine.go

@@ -131,7 +131,8 @@ type Engine struct {
 // Init initializes the struct. This is the first call you must make. Do not
 // proceed with calls to other methods unless this succeeds first. This also
 // loads all the functions by calling Init on each one in the graph.
-// TODO: should Init take the graph as an input arg to keep it as a private field?
+// TODO: should Init take the graph as an input arg to keep it as a private
+// field?
 func (obj *Engine) Init() error {
 	obj.ag = make(chan error)
 	obj.agLock = &sync.Mutex{}