Repr formatter with ShowRepr trait

Hi Armin,

The python repr that is (almost) always is single line is nice. This means that it’s safe to put in logs or print to console, even if value is something that is got from third party.

For example if you are printing error value:

print("Server returned bad response: ", repr(e))

It’s guaranteed that it will never print:

Server returned bad response:

[ ... 1000 newlines ... ] 

Something wrong happened, but it can be fixed if you run:
sudo rm -rf /