Particles fix

Changes:
Added led-strip-particles.cpp & .h
Updated particles() function in firmware/spark-neopixel-control.ino
Moved config.json to config.example.json and added to .gitignore

WARNING:  Back up your config.json if you care about it because it's about to be deleted. I added config.example.json, which can be copied to config.json afterwards.

![spark-io-particles](https://cloud.githubusercontent.com/assets/6699/5053710/f56d6b9c-6c01-11e4-9fb5-f8e93ff6b6fa.png)