log: add Log::setPattern()

include/villas/log.hpp

@@ -68,6 +68,7 @@ public:
 
 	Logger get(const std::string &name);
 
+	void setPattern(const std::string &pattern);
 	void setLevel(Level lvl);
 	void setLevel(const std::string &lvl);
 

lib/log.cpp

@@ -134,6 +134,13 @@ void Log::parse(json_t *cfg)
 	}
 }
 
+void Log::setPattern(const std::string &pat)
+{
+	pattern = pat;
+
+	spdlog::set_pattern(pattern, spdlog::pattern_time_type::utc);
+}
+
 void Log::setLevel(Level lvl)
 {
 	spdlog::set_level(lvl);