[thin_dump] --format custom=<shared lib>

Allow people to use their own emitters held in a shared library.

Put a trivial emitter in contrib/ as an example.

thin-provisioning/shared_library_emitter.h

@@ -0,0 +1,14 @@
+#ifndef THIN_PROVISIONING_SHARED_LIBRARY_EMITTER_H
+#define THIN_PROVISIONING_SHARED_LIBRARY_EMITTER_H
+
+#include "thin-provisioning/emitter.h"
+
+//----------------------------------------------------------------
+
+namespace thin_provisioning {
+	emitter::ptr create_custom_emitter(std::string const &shared_lib, std::ostream &out);
+}
+
+//----------------------------------------------------------------
+
+#endif