move shared functions to global errors and utils modules
fix dicttoxml to take an arbitrarily nested dictionary and transform it to xml
restructure -- move api connectors to api module, inherit from base api connector, keep global functions etc.. in usps module
more fixes to dicttoxml, add tracking wrapper
better docstrings
add service standards api and tests, make xmltodict recursive
response to review
API doesn't always need to be a method
get tests passing for all APIs
changes to setup.py
new service standards method to return a service estimate for a given set of package data and postal shipping method code