Because eboot first erases the space required for the new sketch, and
if the new sketch is larger then the old one, with the old way, part of
the beginning of new sketch will be deleted. Therefore for now I opted
to keep the max update size either half the available space for
sketches or what's left from the first one, whichever is smaller.
To be able to create a simple post mechanism for updates, I needed to
have a way to write the new binary, without knowing it's final size, so
I added an option to the end() method. Example in the WebServer
examples.
