Default to capital letters for log level.

src/common.cxx

@@ -45,6 +45,6 @@ namespace logging {
   }
   
   std::ostream & operator<<(std::ostream & os, level l) {
-    return os << std::string(level_to_string(l));
+    return os << std::string(to_string(l, true));
   }
 }

src/loggers/json_layout.cxx

@@ -58,7 +58,7 @@ void json_layout::format(std::ostream & os, logpacket const & pkt) const {
   Json::Value root;
   root["instant"]["epochSecond"] = (Json::UInt64) pkt.time.tv_sec;
   root["instant"]["nanoOfSecond"] = pkt.time.tv_usec * 1000;
-  root["level"] = level_to_string(pkt.level);
+  root["level"] = to_string(pkt.level, true);
   root["loggerName"] = pkt.logger;
   if (log_as_json_) {
     root["message"] = pkt.message.json();

test/json_layout_test.cxx

@@ -29,13 +29,13 @@ std::string const formatted_output = R"({
     "epochSecond" : 1554401840,
     "nanoOfSecond" : 123456000
   },
-  "level" : "warning",
+  "level" : "WARNING",
   "loggerName" : "UnitTest",
   "message" : "This is a test message"
 })";
 
 std::string const compact_output = "{\"instant\":{\"epochSecond\":"
-  "1554401840,\"nanoOfSecond\":123456000},\"level\":\"warning\","
+  "1554401840,\"nanoOfSecond\":123456000},\"level\":\"WARNING\","
   "\"loggerName\":\"UnitTest\",\"message\":\"This is a test message\"}";
 
 TEST(JsonLayoutTest, LogsInformationInJSON) {
@@ -89,7 +89,7 @@ std::string const struct_output = R"({
     "epochSecond" : 1554401840,
     "nanoOfSecond" : 123456000
   },
-  "level" : "warning",
+  "level" : "WARNING",
   "loggerName" : "UnitTest",
   "message" : "{225}"
 })";
@@ -106,7 +106,7 @@ std::string const struct_json_output = R"({
     "epochSecond" : 1554401840,
     "nanoOfSecond" : 123456000
   },
-  "level" : "warning",
+  "level" : "WARNING",
   "loggerName" : "UnitTest",
   "message" : {
     "content" : 225