Wrapping print builtin

[jayvdb]

The next component of #59 is coala's context managers that replace the print builtin.

It is a bit buggy, as explained at https://gitlab.com/coala/coala-utils/issues/93

The use case is when interacting with a running application where references to the real sys streams have been added to various objects , and the test logic does not want to, or can not, destroy everything before the test. And the app code uses print(..., file=stream). If it uses stream.write, this wont help.