This change improves read performance when massive data is sent
via USB by exploiting the hardware capability to handle multi-packet
transfers autonomously.

It makes no sense to have ::recv calling repeatedly ::read in this
case.

Now the release() function only performs the action that is called for,
i.e. release the endpoint and let it receive data. All the buffers handling
has been inlined in the callers, this also slightly improves performance
because it allows to remove some redundant checks.

The reference to the upper USBDevice class is passed on
the EPHandler constructor.

this is the proper type to encapsulate a byte when data is available
or -1 when there is no data.

Port of https://github.com/arduino/Arduino/pull/4718 to SAMD core.

Fix #149

Port of https://github.com/arduino/Arduino/pull/4996

Previous 0 was always returned.

Change digitalPinToInterrupt to return pin, and use g_APinDescription[pin].ulExtInt to map pin inside attachInterrupt/detachInterrupt

This brings things inline with the atachInterrupt documentation for
usage:
attachInterrupt(digitalPinToInterrupt(pin), ISR, mode);