Spark Core v0.2.4

Spark Core v0.2.4 includes one major change: we added a buffer to the MISO line of the CC3000 because the CC3000 and SPI FLASH module share the same SPI lines.

The CC3000 MISO line is a pull-up line when the CC3000 is not communicating. This means that, if another device is communicating on the same line, its voltages are higher than expected; in our case, the SPI FLASH module was communicating at 3.3V high and 1.4V low (instead of 3.3V and 0V).

The SPI FLASH module seemed to still communicate correctly; we could read, write, and erase without encountering any errors. However, it's possible that issues might develop in the long run or in extreme cases, so we implemented a permanent fix: adding a buffer to the MISO line.

We also made 3V3 and GND fixes opportunistically as we re-routed traces on the board.

Thanks to @ladyada for pointing out this bug!

NOTE: This release has been tagged as a pre-release because a flaw in the buffer design would cause the CC3000 to be incommunicative. So don't use this one :-)