fix golint comments warnings

comment/comment.go

@@ -2,12 +2,15 @@ package comment
 
 import "github.com/z7zmey/php-parser/node"
 
+// Comment represents comment lines in the code
 type Comment interface {
 	String() string
 }
 
+// Comments a collection of comment groups assigned to nodes
 type Comments map[node.Node][]Comment
 
+// AddComments add comment group to the collection
 func (c Comments) AddComments(node node.Node, comments []Comment) {
 	c[node] = append(c[node], comments...)
 }

comment/doc_comment.go

@@ -1,9 +1,11 @@
 package comment
 
+// DocComment represents comments that start /**
 type DocComment struct {
 	value string
 }
 
+// NewDocComment - DocComment constructor
 func NewDocComment(value string) *DocComment {
 	return &DocComment{
 		value,

comment/plain_comment.go

@@ -1,9 +1,11 @@
 package comment
 
+// PlainComment represents comments that dont start /**
 type PlainComment struct {
 	value string
 }
 
+// NewPlainComment - PlainComment constructor
 func NewPlainComment(value string) *PlainComment {
 	return &PlainComment{
 		value,