first stab at travis continuos integration builds
smartly use .replace & remove 'io' dep. for py2

here goes backwards compatibility testing for py2 versions -- though I have them all locally, trying for travis CI which would help identify problems going forward. I'm sure there is some six.PY3 things to work out yet, already noticed I need a from __future__ import for the 'with' contextmanager for python 2.5.