Improve logging: color, ms timestamps, PID, thread id via environment variable

Set VIRCADIA_LOG_OPTIONS to a string containing these keywords:

	color
	milliseconds
	process_id
	thread_id

The separator doesn't matter. Example:

    $ export VIRCADIA_LOG_OPTIONS="color milliseconds"

libraries/shared/src/LogHandler.cpp

@@ -32,6 +32,26 @@ LogHandler& LogHandler::getInstance() {
     return staticInstance;
 }
 
+LogHandler::LogHandler() {
+    QString log_options = qgetenv("VIRCADIA_LOG_OPTIONS").toLower();
+
+    if (log_options.contains("color")) {
+        _useColor = 1;
+    }
+
+    if (log_options.contains("process_id")) {
+        _shouldOutputProcessID = true;
+    }
+
+    if (log_options.contains("thread_id")) {
+        _shouldOutputThreadID = true;
+    }
+
+    if (log_options.contains("milliseconds")) {
+        _shouldDisplayMilliseconds = true;
+    }
+}
+
 const char* stringForLogType(LogMsgType msgType) {
     switch (msgType) {
         case LogInfo:
@@ -51,6 +71,29 @@ const char* stringForLogType(LogMsgType msgType) {
     }
 }
 
+const char* colorForLogType(LogMsgType msgType) {
+    switch (msgType) {
+        case LogInfo:
+            return "\u001b[37;1m";  // Bold white
+        case LogDebug:
+            return "";
+        case LogWarning:
+            return "\u001b[35;1m";  // Bright magenta
+        case LogCritical:
+            return "\u001b[31;1m";  // Bright red
+        case LogFatal:
+            return "\u001b[31;1m";  // Bright red
+        case LogSuppressed:
+            return "";
+        default:
+            return "";
+    }
+}
+
+const char* colorReset() {
+    return "\u001b[0m";
+}
+
 // the following will produce 11/18 13:55:36
 const QString DATE_STRING_FORMAT = "MM/dd hh:mm:ss";
 
@@ -133,7 +176,15 @@ QString LogHandler::printMessage(LogMsgType type, const QMessageLogContext& cont
 
     QString logMessage = QString("%1 %2\n").arg(prefixString, message.split('\n').join('\n' + prefixString + " "));
 
-    fprintf(stdout, "%s", qPrintable(logMessage));
+    const char* color = "";
+    const char* resetColor = "";
+
+    if (_useColor) {
+        color = colorForLogType(type);
+        resetColor = colorReset();
+    }
+
+    fprintf(stdout, "%s%s%s", color, qPrintable(logMessage), resetColor);
 #ifdef Q_OS_WIN
     // On windows, this will output log lines into the Visual Studio "output" tab
     OutputDebugStringA(qPrintable(logMessage));

libraries/shared/src/LogHandler.h

@@ -57,7 +57,7 @@ public:
     void setupRepeatedMessageFlusher();
 
 private:
-    LogHandler() = default;
+    LogHandler();
     ~LogHandler() = default;
 
     void flushRepeatedMessages();
@@ -66,6 +66,7 @@ private:
     bool _shouldOutputProcessID { false };
     bool _shouldOutputThreadID { false };
     bool _shouldDisplayMilliseconds { false };
+    bool _useColor { false };
 
     int _currentMessageID { 0 };
     struct RepeatedMessageRecord {