Update KeyPad.md

* Added Caveats section
* Moved warning about multiple keys there
* Added note in caveats section that the module sets watches on columns (in light of STMF103 limit on watches on pins with same numbers) - I had been tearing my hair out a while back with some keys sometimes stopping working, and then it fixed itself when I moved some things around. Much later I realized the watch set by the DHT was clobbering one of the column watches. 
* Added example for the 4x5 keypads available on Ebay and a link to a picture of them.
Update AT24.js

Fix handling of i2ca; No longer create global if i2ca argument not specified, and corrected tests for argument being undefined. 

Add writel() to write blocks of any length.
Update KeyPad.md

Moved the 4x5 image up next to the 4x4 one.
Add image of the 5x4 keypad. These are pretty cool keypads for projects, as they suggest a user interface.
Update AT24.md

Document writel(), add column to list equivalent parts.
Create Font6x12.js

6x12 font, like the other font modules.
Create Font8x16.js

8x16 font, like the other font modules.
Update Font6x12.js

What's the year again?
Update KeyPad.md

Where'd that comma come from?
Update AT24.js

Updated comments regarding writel()
Update Font6x12.js

oops
Merge pull request #67 from SpenceKonde/master

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