ext/wavpack/: Add wavpack encoder element (#343131).

ext/wavpack/: Add wavpack encoder element (#343131).

Original commit message from CVS:
Patch by: Sebastian Dröge  <mail at slomosnail de>
* ext/wavpack/Makefile.am:
* ext/wavpack/gstwavpack.c: (plugin_init):
* ext/wavpack/gstwavpackcommon.h:
* ext/wavpack/gstwavpackenc.c: (gst_wavpack_enc_mode_get_type),
(gst_wavpack_enc_correction_mode_get_type),
(gst_wavpack_enc_joint_stereo_mode_get_type),
(gst_wavpack_enc_base_init), (gst_wavpack_enc_class_init),
(gst_wavpack_enc_init), (gst_wavpack_enc_dispose),
(gst_wavpack_enc_sink_set_caps), (gst_wavpack_enc_set_wp_config),
(gst_wavpack_enc_format_samples), (gst_wavpack_enc_push_block),
(gst_wavpack_enc_chain), (gst_wavpack_enc_rewrite_first_block),
(gst_wavpack_enc_sink_event), (gst_wavpack_enc_change_state),
(gst_wavpack_enc_set_property), (gst_wavpack_enc_get_property),
(gst_wavpack_enc_plugin_init):
* ext/wavpack/gstwavpackenc.h:
* ext/wavpack/md5.c:
* ext/wavpack/md5.h:
Add wavpack encoder element (#343131).