I2C and JTAG fixes

Fix I2C stop violation and set_dtr_rts wrong command

Use optional SMBbus mode scanning

Fix GPIO `set_direction` and fix virtual backend

Fix GPIO initial values

Improved support for EEPROM, GPIO and virtual test framework

Rework and improve GPIO APIs

Add custom VID/PID support to PyFtdi tools

Fix compatibility with Python3.5 which lacks IntFlag

Add APIs to force-drive SPI /CS