all: use fixdocs tool to store package documentation in doc.go

Add copyright header to doc.go

graph/formats/dot/ast/ast.go

@@ -8,8 +8,6 @@
 // This file is made available under a Creative Commons CC0 1.0
 // Universal Public Domain Dedication.
 
-// Package ast declares the types used to represent abstract syntax trees of
-// Graphviz DOT graphs.
 package ast // import "gonum.org/v1/gonum/graph/formats/dot/ast"
 
 import (