Add long write to AT24, keypad docs, more fonts. 

Add picture of 5x4 keypad, add it to keypad module doc, added notice to keypad doc that it sets watches on the columns (of course it does - but you can get caught off guard by the no-two-watches-on-pin-with-same-number bit easily). 

Added 6x12 and 8x16 fonts. 

Added writel() to AT24.js, to write data of arbitrary length.