Add python six module for python compatibility

[lynneatan]

Addressing issue #19 Error in extract_cursor() method (#19)
Problem:

• Users using python 2.7 can't retrieve all pledges to a campaign because the api returns a dict with unicode instead of string which causes an error to be thrown when iterating through a creator's pages ( see api.py line 73 for reference)

Solution:

• Import the python six module that allows the conditional to handle both unicode and string (six.text_type)
• Also removed the urllib_parse file and replaced it with six imports instead

[emosesPatreon]

Can you get this from six.moves as well? Maybe version_compatibility can go away.

[lynneatan]

I unfortunately didn't find any six documentation for timezone compatibility

[emosesPatreon]

I don't see a change to requirements.txt here. You'll want to update it with six. pip freeze -r requirements.txt should do it.

[jrsun]

tiny comment! otherwise looks great 💯

[jrsun]

let's just replace type(current_dict) != str on line 73 with this check.