a transparent color, by Dmitry A. Shashkin
 *       Smooth rescaling, by Kostas Michalopoulos
 * v1.8: Set max length to customize number of live points in the dataset with options.maxDataSetLength, by Krishna Narni
 * v1.9: Display timestamps along the bottom, by Nick and Stev-io
 *       (https://groups.google.com/forum/?fromgroups#!topic/smoothie-charts/-Ywse8FCpKI%5B1-25%5D)
 *       Refactored by Krishna Narni, to support timestamp formatting function
 * v1.10: Switch to requestAnimationFrame, removed 