Fix transposed distinctP arguments

The dictionary entry for eq gets passed in first. There was also a
function arity issue with the definition that would quietly fail because
javascript coerces functions to true ( ͡° ͜ʖ ͡°)
Merge pull request #15 from MichaelXavier/distinct-transposed-arguments

Fix transposed distinctP arguments
Subscribers should always get the current value immediately when subscribing.
Merge branch 'master' of github.com:bodil/purescript-signal
Because subscribe now yields immediately, foldp's initial loop value
should just be seed.
Generalise zip to take a transform function.
Unit tests at last.
Release 2.0.0
Sync API doc.