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

Add copyright header to doc.go

Keep original comment style (e.g. line comments and block comments).

stat/sampleuv/sample.go

@@ -2,12 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package sampleuv implements advanced sampling routines from explicit and implicit
-// probability distributions.
-//
-// Each sampling routine is implemented as a stateless function with a
-// complementary wrapper type. The wrapper types allow the sampling routines
-// to implement interfaces.
 package sampleuv // import "gonum.org/v1/gonum/stat/sampleuv"
 
 import (