Move Config and ACL to the top-level module (libp2p#20)

I would like to programatically generate relays configurations, however this
is slightly more difficult because, despite being exported types, they are in
the "main" package.

This PR moves them to the top-level directory so that they can be imported from
other modules.

I also took the liberty of documenting things.

config.go

@@ -67,6 +67,8 @@ type TLSConfig struct {
 	KeyPairPaths [][2]string
 }
 
+// DefaultConfig returns a default relay configuration using default resource
+// settings and no ACLs.
 func DefaultConfig() Config {
 	return Config{
 		Network: NetworkConfig{

identity.go

@@ -2,9 +2,10 @@ package relaydaemon
 
 import (
 	"fmt"
+	"io/ioutil"
 	"os"
 
-	"github.com/libp2p/go-libp2p/core/crypto"
+	"github.com/libp2p/go-libp2p-core/crypto"
 )
 
 // LoadIdentity reads a private key from the given path and, if it does not
@@ -22,7 +23,7 @@ func LoadIdentity(idPath string) (crypto.PrivKey, error) {
 
 // ReadIdentity reads a private key from the given path.
 func ReadIdentity(path string) (crypto.PrivKey, error) {
-	bytes, err := os.ReadFile(path)
+	bytes, err := ioutil.ReadFile(path)
 	if err != nil {
 		return nil, err
 	}
@@ -42,7 +43,7 @@ func GenerateIdentity(path string) (crypto.PrivKey, error) {
 		return nil, err
 	}
 
-	err = os.WriteFile(path, bytes, 0400)
+	err = ioutil.WriteFile(path, bytes, 0400)
 
 	return privk, err
 }