Add MIME StreamEncoding enum val

pgpainless-core/src/main/java/org/pgpainless/algorithm/StreamEncoding.java

@@ -32,6 +32,17 @@ public enum StreamEncoding {
      */
     UTF8(PGPLiteralData.UTF8),
 
+    /**
+     * The literal data packet contains a MIME message body part (RFC2045).
+     * Introduced in rfc4880-bis10.
+     *
+     * TODO: Replace 'm' with 'PGPLiteralData.MIME' once BC 1.71 gets released and contains our fix:
+     *  https://github.com/bcgit/bc-java/pull/1088
+     *
+     * @see <a href="https://tools.ietf.org/id/draft-ietf-openpgp-rfc4880bis-10.html#name-literal-data-packet-tag-11">RFC4880-bis10</a>
+     */
+    MIME('m'),
+
     /**
      * Early versions of PGP also defined a value of 'l' as a 'local' mode for machine-local conversions.
      * RFC 1991 [RFC1991] incorrectly stated this local mode flag as '1' (ASCII numeral one).