Various optimizations and refactoring of pupilFitter.h

- removed overloaded functions for getcandidates and refinepoints: resulting function now only uses Opencv's Point instead of Point2f
- added getDarkestPixelBetter to replace getDarkestPixel: this handles cases where glints cause very dark pixels to appear (primarily in the Vive benchmark videos). This also makes pupil detection slightly more robust.
- added initial glint handling code to refinePoints (not currently active)
- misc documentation