Port of
https://github.com/arduino/Arduino/commit/6a6ed3d10ad1470283d7771906ce81
ad97fa06f0

USBHost used to have an init() method that now is incorporated in
Init(). The leftover init() calls in the library were calling
the init() function in the variant files instead (that has nothing
to do with the USBHost library).

Removing the calls to init() fix it.

Fix #115

0x00 CTRL-@ through 0x1F CTRL-_

Also return ASCII codes for keys: ESCAPE, DELETE, TAB, and BACKSPACE keys.
Return correct code for ENTER and keypad ENTER keys.

https://github.com/felis/USB_Host_Shield_2.0/pull/185

Affects all devices that do IN transfers.

Followed the precedent in SPI and Wire libraries, adding #ifdefs to conditionally declare Wire interface externs

Bulk endpoints were incorrectly shown as Interrupt.

See https://github.com/arduino/Arduino/pull/4225

Adjust requestFrom, endTransmission, and startTransmissionWire to handle
repeated starts

In the wire library there are several functions where
an unnecessarily complex coding has been used:

  - endTransmission: the availability of data is already
    checked in while(...), therefore need not be checked
    again in the loop.
  - requestFrom: the for-loop has a predefined and fixed
    number of loops. Therefore a check whether the last
    element has been reached is unnecessary and does not
    add any benefit.

Fixes #20