acme: expose internal/acme as acme package

This moves all of internal/acme into the acme package,
making the lower level API accessible by any other package.

Fixes golang/go#16938.

Change-Id: Ie35f4b6b6b42ebb7fb4ad03ba067df8c3063feff
Reviewed-on: https://go-review.googlesource.com/28297
TryBot-Result: Gobot Gobot <gobot@golang.org>
Run-TryBot: Alex Vaghin <ddos@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

acme/acme.go

@@ -6,6 +6,10 @@
 // Automatic Certificate Management Environment (ACME) spec.
 // See https://tools.ietf.org/html/draft-ietf-acme-acme-02 for details.
 //
+// Most common scenarios will want to use autocert subdirectory instead,
+// which provides automatic access to certificates from Let's Encrypt
+// and any other ACME-based CA.
+//
 // This package is a work in progress and makes no API stability promises.
 package acme
 

acme/autocert/autocert.go

@@ -27,7 +27,7 @@ import (
 	"sync"
 	"time"
 
-	"golang.org/x/crypto/acme/internal/acme"
+	"golang.org/x/crypto/acme"
 	"golang.org/x/net/context"
 )
 

acme/autocert/autocert_test.go

@@ -24,7 +24,7 @@ import (
 	"testing"
 	"time"
 
-	"golang.org/x/crypto/acme/internal/acme"
+	"golang.org/x/crypto/acme"
 	"golang.org/x/net/context"
 )