Escape the headers using RFC2047

Incorporates the encoding code from rfc2047.erl from Zotonic to encode
the Subject: header. Also adds parser for RFC 822-style address lists;
encode all header values with RFC2047.

Squashed commit of the following:

commit 5573728e0eed403b919d947c5ee30fb6c6554dbb
Author: Arjan Scherpenisse <arjan@scherpenisse.net>
Date:   Mon Nov 5 23:05:25 2012 +0100

    Add test with decode_header

commit 749b140dd9f75dd327ab7ee63af72fa78e313ade
Author: Arjan Scherpenisse <arjan@scherpenisse.net>
Date:   Mon Nov 5 21:49:13 2012 +0100

    Add parser for RFC 822-style address lists; encode all header values with RFC2047.

commit b9f1196f48215e9780c632e630cdf5b57d343265
Author: Arjan Scherpenisse <arjan@scherpenisse.net>
Date:   Mon Nov 5 15:59:32 2012 +0100

    Escape the Subject: header using RFC2047

    Incorporates the encoding code from rfc2047.erl from Zotonic to encode
    the Subject: header.