Callbacks not handled correctly when DIAGNOSTICS not defined.

[Mikal Hart]

Due to a misunderstanding about how the "weak" attribute works, on certain platforms, sketches that do not have the callback functions defined crash.

Specifically, having a "weak" function declared and then not implementing it (weak or strong) anywhere, does not allow you to write code like this:

   if (ISBDConsoleCallback != NULL)
   {
         ISBDConsoleCallback(this, c);
   }

[Mikal Hart]

Fixed in release 2.0.0!