Refactoring

Made the following name changes:
the type synonym Event (meaning Maybe) is now SEvent
display' is now display
display is now displayStr
init is now delay (in exposed code such as examples and in the default
Euterpea)
delay is now fdelay (fixed delay)
delayt is now vdelay (variable delay)

timer now produces an event stream rather than a continuous Bool steam.
timer and the delays are now exported from Control.SF.AuxFunctions (and
also reexported from Euterpea).

A new mediator was added:
genEvents :: ArrowInit a => [b] -> a (Time, Double) (SEvent b)

The cabal file was updated to put examples in the right places.