[dbg] Pull out common code into dbg-lib

- Modularize common routines
- Extract the block_dumper interface for displaying blocks
- Remove inheritance from show_traits

dbg-lib/output_formatter.h

@@ -0,0 +1,37 @@
+#ifndef DBG_OUTPUT_FORMATTER_H
+#define DBG_OUTPUT_FORMATTER_H
+
+#include <boost/lexical_cast.hpp>
+#include <boost/optional.hpp>
+#include <boost/tuple/tuple.hpp>
+#include <boost/variant.hpp>
+
+#include <vector>
+#include <string>
+
+//----------------------------------------------------------------
+
+namespace dbg {
+	class formatter {
+	public:
+		typedef std::shared_ptr<formatter> ptr;
+
+		virtual ~formatter() {}
+		virtual void field(std::string const &name, std::string const &value) = 0;
+		virtual void child(std::string const &name, formatter::ptr t) = 0;
+		virtual void output(std::ostream &out, int depth = 0,
+				    boost::optional<std::string> name = boost::none) = 0;
+	};
+
+	template <typename T>
+	void
+	field(formatter &t, std::string const &name, T const &value) {
+		t.field(name, boost::lexical_cast<std::string>(value));
+	}
+
+	formatter::ptr create_xml_formatter();
+}
+
+//----------------------------------------------------------------
+
+#endif