Support for 'delay' keyword in the stutter method (Players)

[aguillon]

Players.stutter allows to change some attribute of the generated events using patterns, for example:

p1 >> play("  *   ", lpf=10000).every(1, "stutter", 10, lpf=10000*(0.7**PRange(10)))

but the events are all too close and the result is somewhat confused. This patchs allows to write

p1 >> play("  *   ", lpf=10000).every(1, "stutter", 10, lpf=10000*(0.7**PRange(10)), delay=0.1225)

which separates the events with an additional period of time (I find it nicer to the ear!). There is also some support for Patterns, e.g.

p1 >> play("  *   ", lpf=10000, delay=0.1).every(1, "stutter", 5, lpf=10000*(0.5**PRange(5)), delay=0.1 * PRange(5))

but this may need some additional testing.