Implement simple hardware I2C support.

i2c_hw: Remove debug code, add include guards etc.
Implement an I2C HD44780 LCD interface.

lcd_hd44780: In LCDInterface_I2C, only commit status when absolutely necessary.

lcd_hd44780: Remove debug code.

lcd_hd44780: Add a comment.
lcd_hd44780: Add I2C-based example.
lcd_hd44780: Use a templated backpack struct
lcd_hd44780: Implement LcdBackPack structs using template specialization
Merge pull request #16 from megari/i2c_stuff_rebased

I2C hardware support and I2C LCD backpack support.