Implement vitastor-cli serve command to serve simple HTTP API

src/util/str_util.h

@@ -34,5 +34,6 @@ std::string addslashes(const std::string & str, const char *toescape = "\\\"");
 std::string realpath_str(std::string path, bool nofail = true);
 std::string format_datetime(uint64_t unixtime);
 bool is_zero(void *buf, size_t size);
+std::string urldecode(const std::string & orig);
 
 #pragma GCC visibility pop