Handle MIME encoded addresses in address book

When addresses contain special characters, net/mail MIME-encodes them
to a valid RFC 5322 address for use in headers. However, these are not
pleasant for human consumption, so we decode them for use in the
completion list. Aerc properly encodes addresses when the message is
sent.

This patch also removes surrounding white space from contact names, if
present.

completer/completer.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"mime"
 	"net/mail"
 	"os/exec"
 	"strings"
@@ -139,13 +140,22 @@ func readCompletions(r io.Reader) ([]string, error) {
 		parts := strings.SplitN(line, "\t", 3)
 		if addr, err := mail.ParseAddress(parts[0]); err == nil {
 			if len(parts) > 1 {
-				addr.Name = parts[1]
+				addr.Name = strings.TrimSpace(parts[1])
 			}
-			completions = append(completions, addr.String())
+			decoded, err := decodeMIME(addr.String())
+			if err != nil {
+				return nil, fmt.Errorf("could not decode MIME string: %w", err)
+			}
+			completions = append(completions, decoded)
 		}
 	}
 }
 
+func decodeMIME(s string) (string, error) {
+	var d mime.WordDecoder
+	return d.DecodeHeader(s)
+}
+
 func (c *Completer) handleErr(err error) {
 	if c.errHandler != nil {
 		c.errHandler(err)