Improve performance when typing passwords

This MR has the following changes that improve performance for me:

1. implement a more efficient algorithm for drawing filled circles

2. reduce keyboard repeat delay from 100ms --> 25ms

3. draw 3 times when using hw accel, since some drivers appear to triple buffer and skip frames on the screen

Measurements from gprof in the first commit in this MR: !98 (diffs)

Fix #103 (closed)