recognize more charsets than utf-8/iso-8859-1/us-ascii when parsing message headers with address

as they occur in From/To headers, for example: "From:
=?iso-8859-2?Q?Krist=FDna?= <k@example.com>".  we are using net/mail to parse
such headers. most address-parsing functions in that package will only decode
charsets utf-8, iso-8859-1 and us-ascii. we have to be careful to always use
net/mail.AddressParser with a WordDecoder that understands more that the
basics.

for issue #204 by morki, thanks for reporting!

message/addr_test.go

@@ -0,0 +1,11 @@
+package message
+
+import (
+	"testing"
+)
+
+func TestParseAddressList(t *testing.T) {
+	l, err := ParseAddressList("=?iso-8859-2?Q?Krist=FDna?= <k@example.com>, mjl@mox.example")
+	tcheck(t, err, "parsing address list")
+	tcompare(t, l, []Address{{"Kristýna", "k", "example.com"}, {"", "mjl", "mox.example"}})
+}