def str(self, string):
return ColorfulString(string, string)<EOL>
Create a new ColorfulString instance of the given
unstyled string.

This method should be used to create a ColorfulString
which is actually not styled yet but can safely be concatinated
with other ColorfulStrings like:

>>> s = colorful.str('Hello ')
>>> s =+ colorful.black('World')
>>> str(s)
'Hello \033[30mWorld\033[39m'

:param str string: the string to use for the ColorfulString