refactor msg formatting, add CLUTCHDUMP

- remove show_* methods.

tests/t-dump.cpp

@@ -0,0 +1,18 @@
+#include <iostream>
+
+#include "../clutchlog/clutchlog.h"
+
+int main(/*const int argc, char* argv[]*/)
+{
+#ifdef WITH_CLUTCHLOG
+
+    auto& log = clutchlog::logger();
+
+    log.out(std::clog);
+    log.threshold(clutchlog::level::xdebug);
+
+    std::vector<std::string> msg = {"hello", "world", "!"};
+
+    CLUTCHDUMP(xdebug, msg);
+#endif
+}