Add stream operator

[ytoml]

Fixes #170 .

Hi, I implemented stream operator.

Changes proposed in this PR:

• Stream operator is enabled, for example:

  
  Point = Class {x = Int; y = Int}
  Point.
  new x, y = Point::__new__ {x; y}
  norm self = self::x**2 + self::y**2

print! 1 |> Point.new(10) |> .norm() # prints 101

@mtshiba

[mtshiba]

Thank you. But I found a mistake in the parsing.

print!(1 + 1 |> f())
print!(1 + 1 |> .abs())

should be

print!(f(1+1))
print!((1+1).abs())

but we got

[ytoml]

Thanks, I fixed it by collecting binop(Expr Op Expr) into single Expr before parsing a pipe op, in order to confirm that all BinOps precede pipes.

[ytoml]

stream.er:

[mtshiba]

Thank you!