Release 0.8: better I2C controller support

* fix detecting hardware in bootloader mode
* added 30ms delay between command retries to allow ECU firmware to detect timeout
* added i2c_get_smbus method that returns an SMBus-like object for transparent I2C communication with ECU in controller mode
* added i2c_speed attribute to configure I2C clock speed for ECU in controller mode
* added command write and response read times to debug logging