cli, docs: Add a docs command for doc generation

This took a lot longer than it looks to get right. It's not perfect, but
it now reliably generates documentation which we can put into gohugo.

engine/resources/msg.go

@@ -52,9 +52,15 @@ type MsgRes struct {
 
 	init *engine.Init
 
-	Body     string            `lang:"body" yaml:"body"`
-	Priority string            `lang:"priority" yaml:"priority"`
-	Fields   map[string]string `lang:"fields" yaml:"fields"`
+	// Body is the body of the message to send.
+	Body string `lang:"body" yaml:"body"`
+
+	// Priority is the priority of the message. Currently this is one of:
+	// Emerg, Alert, Crit, Err, Warning, Notice, Info, Debug.
+	Priority string `lang:"priority" yaml:"priority"`
+
+	// Fields are the key/value pairs set in the journal if we are using it.
+	Fields map[string]string `lang:"fields" yaml:"fields"`
 
 	// Journal should be true to enable systemd journaled (journald) output.
 	Journal bool `lang:"journal" yaml:"journal"`

engine/resources/noop.go

@@ -49,7 +49,8 @@ type NoopRes struct {
 
 	init *engine.Init
 
-	Comment string `lang:"comment" yaml:"comment"` // extra field for example purposes
+	// Comment is a useless comment field that you can use however you like.
+	Comment string `lang:"comment" yaml:"comment"`
 }
 
 // Default returns some sensible defaults for this resource.

engine/resources/print.go

@@ -52,7 +52,9 @@ type PrintRes struct {
 
 	init *engine.Init
 
-	Msg string `lang:"msg" yaml:"msg"` // the message to display
+	// Msg is the message to display.
+	Msg string `lang:"msg" yaml:"msg"`
+
 	// RefreshOnly is an option that causes the message to be printed only
 	// when notified by another resource. When set to true, this resource
 	// cannot be autogrouped.

engine/resources/test.go

@@ -70,6 +70,7 @@ type TestRes struct {
 	Uint64 uint64 `lang:"uint64" yaml:"uint64"`
 
 	//Uintptr uintptr `lang:"uintptr" yaml:"uintptr"`
+
 	Byte byte `lang:"byte" yaml:"byte"` // alias for uint8
 	Rune rune `lang:"rune" yaml:"rune"` // alias for int32, represents a Unicode code point
 
@@ -84,7 +85,7 @@ type TestRes struct {
 	Int8Ptr   *int8   `lang:"int8ptr" yaml:"int8ptr"`
 	Uint8Ptr  *uint8  `lang:"uint8ptr" yaml:"uint8ptr"`
 
-	// probably makes no sense, but is legal
+	// Int8PtrPtrPtr probably makes no sense, but is legal.
 	Int8PtrPtrPtr ***int8 `lang:"int8ptrptrptr" yaml:"int8ptrptrptr"`
 
 	SliceString []string          `lang:"slicestring" yaml:"slicestring"`