+ added a small 'fisrt steps' section.
+ comments about how/why not implement |.
+ new Capture object is used to mark that the output should be captured as it is default in sh.
* _out/_err=None means it goes to /dev/null.
+ polute more the builtins.
* rename because it clashed with Python3's module of the same name.
+ more examples
+ more output tests covering None and Capture.
+ more discussion.