XO Stick

Notes on v5:

- ATtiny261A should be at least ATtiny461a if not ATtiny861a, since

 USB library takes up 2496 bytes.

- full size USB convert to mini or micro? (no through-hole micro-B connectors?)

- LED1/LED2 need better polarity mark (flat side is down, towards big usb port)

- use '-kit' suffixed versions of footprints (solder mask on component side)

- break off tab appears to work well.

- island between tabs should be anchored to body, not tabs?

- can we avoid anchors on break off tabs, instead use central anchor?

  ie.
    T
 ------------
|            |
 --          \--
TXT|            |
 --          \--
|            |
 ------------
    T

where T indicates tabs.

- remove symmetry from USB connector placement to allow two tabs on

 XOrduino board.  (ie, move connector all the way down)