Refactor 'stream', add a few examples

[jiribenes]

Update: 'stream' got slightly refactored (using Any everywhere now), fixed a few bugs, added a few examples of push streams, pull streams, their infinite variants, limit, zip, ...

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I added a few examples for the new stream stdlib into examples/stdlib.
I'd also be happy to add some Nice ®️ example into the stream.effekt file itself (either into the doc comments or as a namespace examples { ... } thing)

I couldn't figure out how to use take properly in a sane (nice idiomatic) way, since it requires me to handle stop and I couldn't find any nicely looking way to do that. Therefore all of these examples are just simple, finite push streams. EDIT: solved

I also tried adding zip in order to iterate through multiple streams in step, but I'm not sure how idiomatic it is (see comments below).

@phischu, please let me know if I'm using the stream library as you envisioned it.
If not, feel free to go ahead and change the examples so that they are closer to what you'd want. :)

TODO (in an ideal world)

• at least one simple example with pull streams
• one example using both pull streams and push streams
• some example with infinite streams
• make zip nicer to use?

[jiribenes]

Also, I just tried using a "for-each" on characters, but it doesn't act the way I'd expect as per the pun:

import stream

def main() = {
  for[Char] { each("Hello") } { c =>
    println(show(c) ++ " (" ++ show(c.toInt) ++ ")")
  }
}

as it prints an infinite stream of:

H (72)
H (72)
H (72)
H (72)
H (72)
H (72)
H (72)
H (72)
H (72)
H (72)
...

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Similarly the code hangs in an infinite loop when I do:

def main() = {
  val list = collectList[Char] { each("Hello") }
  println(list.map { (c: Char) => show(c) })
}

which I'd presume would just output ['H', 'e', 'l', 'l', 'o'].

[jiribenes]

LGTM (modulo small whitespace changes)