USBCore SET_CONFIGURATION handler is not interrupt-safe

In USBCore.cpp, the handleStandardSetup() interrupt subroutine's SET_CONFIGURATION case calls initEndpoints(), which calls initEP(). For Bulk-OUT endpoints, initEP() calls operator new and possibly operator delete. In the absence of any other information, I assume the implementations of those operators internally rely on malloc() and free(), which are not interrupt-safe.

A proper fix requires a fair amount of reorganization. The DoubleBufferedEPOutHandler class object should be created early, during the initialization of the USB device. When a SET_CONFIGURATION request is received, the object should not be deleted and recreated, but properly reset. (This is related to issue #350, although the problem was present before that.)

Start in USBCore.cpp at the handleStandardSetup() interrupt subroutine and trace the SET_CONFIGURATION path through initEndpoints() and initEP(). Inspect how DoubleBufferedEPOutHandler is created and destroyed during USB device initialization and configuration changes. Done means SET_CONFIGURATION no longer performs interrupt-unsafe allocation or deletion and instead resets the existing handler.

Written by the indexing model from the issue text.