Better unicode support for python2

[ryan-collingham]

Many classes have a type schema that validates constructor params. Currently a lot of these validate strings against str, which in python 2 means that unicode strings are not allowed. Most of the time there is not a good reason to disallow unicode strings.

In python 2 the basestring type can be used to check if a string is either str or unicode. For python 3, basesting can be used via from past.builtins import basestring.

[kn-ms]

No more python2 support