add real formatted debug logging with timestamps

src/RedirectablePrint.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <Print.h>
+#include <stdarg.h>
 
 /**
  * A Printable that can be switched to squirt its bytes to a different sink.
@@ -11,6 +12,13 @@ class RedirectablePrint : public Print
 {
     Print *dest;
 
+    /// We dynamically grow this scratch buffer if necessary
+    char *printBuf = new char[64];
+    size_t printBufLen = 64;
+
+    /// Used to allow multiple logDebug messages to appear on a single log line
+    bool isContinuationMessage = false;
+
   public:
     RedirectablePrint(Print *_dest) : dest(_dest) {}
 
@@ -20,6 +28,21 @@ class RedirectablePrint : public Print
     void setDestination(Print *dest);
 
     virtual size_t write(uint8_t c);
+
+    /**
+     * Debug logging print message
+     * 
+     * If the provide format string ends with a newline we assume it is the final print of a single
+     * log message.  Otherwise we assume more prints will come before the log message ends.  This
+     * allows you to call logDebug a few times to build up a single log message line if you wish.
+     * 
+     * FIXME, eventually add log levels (INFO, WARN, ERROR) and subsystems.  Move into 
+     * a different class.
+     */
+    size_t logDebug(const char * format, ...)  __attribute__ ((format (printf, 2, 3)));
+
+    /** like printf but va_list based */
+    size_t vprintf(const char *format, va_list arg);
 };
 
 class NoopPrint : public Print