Support bouncetime

Fixed indexes in i2c_smbus_read_block_data

As usual, the first element in the buffer is the size while the rest is the actual data.

Added pull up/down support

Updated README.md

I2C read_word fixed

Promote to int32 before shifting

UART adaptations for modern Raspbian (uraimo#56)

- Modernized tty naming ("serial0" / "serial1")
- Added 2400 / 4800 speeds
- refactored SysFSUART init() to take a list of devices to try in order of preference (first successful wins)

Added I2C,SPI,UART and updated GPIOs for CHIP

The board supports a sysfs interface for basic PWM functionality too,
but that requires a bit more work.
Note that while I2C and UART will work out of the box, SPI requires a
modified device tree.

Fixed null pointer issue for I2C

Closes uraimo#53.

Cleaned up comments, abort on error opening ADC

Delayed I2C device open

Didn't notice this during testing since I was using SysFSI2C directly,
the I2CInterface objects initialization in the presets was crashing
since /dev/i2c-0 normally does not exist. Moved open(), fd will now be
tested and the device will be opened when needed.