Create RedirectablePrint and NoopPrint for serial debug redirection

src/RedirectablePrint.cpp

@@ -0,0 +1,13 @@
+#include "RedirectablePrint.h"
+#include <assert.h>
+
+/**
+ * A printer that doesn't go anywhere
+ */
+NoopPrint noopPrint;
+
+void RedirectablePrint::setDestination(Print *_dest)
+{
+    assert(_dest);
+    dest = _dest;
+}

src/RedirectablePrint.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <Print.h>
+
+/**
+ * A Printable that can be switched to squirt its bytes to a different sink.
+ * This class is mostly useful to allow debug printing to be redirected away from Serial
+ * to some other transport if we switch Serial usage (on the fly) to some other purpose.
+ */
+class RedirectablePrint : public Print
+{
+    Print *dest;
+
+  public:
+    RedirectablePrint(Print *_dest) : dest(_dest) {}
+
+    /**
+     * Set a new destination
+     */
+    void setDestination(Print *dest);
+
+    virtual size_t write(uint8_t c) { return dest->write(c); }
+};
+
+class NoopPrint : public Print
+{
+  public:
+    virtual size_t write(uint8_t c) { return 1; }
+};
+
+/**
+ * A printer that doesn't go anywhere
+ */
+extern NoopPrint noopPrint;