Enhancement: Add support for REPL sessions

[salabim]

I don;t think this will be possible, at least not in a useful way. I could maybe make an implementation where the left-hand side of a 'pair' is left out, but what's the point of that? Then you can just use print(). But I'm open to better solutions, of course.

[salabim]

Inspired by @PFython 's remarks, I have made ycecream compatible with REPLs, be it with extremely limited functionality:

• all arguments are just presented as such, i.e. no left-hand side, e.g.

  >>> hello = "world"
  >>> y(hello, hello * 2)
  y| 'hello', 'hellohello'
  ('hello', 'hellohello')

• line numbers are never shown
• use as a decorator is not supported
• use as a context manager is not supported