[cmp] add decompression support

* Adds .Z, .gz, .lzma, .xz and .bz2 decompression support for DD images
  using the Bled library (https://github.com/pbatard/bled).
* Closes #269

src/bled/header_skip.c

@@ -0,0 +1,10 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+#include "libbb.h"
+#include "bb_archive.h"
+
+void FAST_FUNC header_skip(const file_header_t *file_header UNUSED_PARAM)
+{
+}