More functions for working with times

[smilack]

When Time.delta was added, the Now and Last newtypes¹ were created to force correct argument order (2a800e2). This works, but timestamps have utility outside of just Deltas, and not having a way to get the current time as a Number or access performance.now() is frustrating.

I don't think Now and Last have to go, but at least exposing performance.now() would be nice because I don't think any other libraries have it.

Here's a workaround using started and stamp:

started :: Effect Last
stamp :: forall a. Last -> (Delta -> a) -> Effect (Stamped a)
type Stamped a = { time :: Number, item :: a }

now :: Effect Number
now = started >>= (_ `stamp` const unit) >>> map _.time

¹ Originally Timestamp Now and Timestamp Prev. At one point, TimestampCurrent and TimestampPrevious.

Proposal

Add and export a function that gives the result of performance.now() as a Number instead of a newtype.

Name?

now is an obvious choice, but it's currently a key in Delta and an obvious choice for pattern matching Now values.

current is probably fine, although I do like pnow (silent p).