task/ta-npi-016-15 -- factor our proxy information into the config

nparcel/conf/nparceld.conf
* placeholder for the new proxy section

nparcel/config.py
* new method proxy_kwargs() which extracts the proxy settings from the
  config file
* new method proxy_string() which constructs a proxy string based on
  the kwargs dictionary that could be fed directly into a HTTP/S header

nparcel/loader.py
* __init__ now accepts proxy and scheme attributes to support proxy
  authentication

nparcel/smser.py
* __init__ now accepts proxy and proxy_scheme attributes to support
  proxy authentication
* factor out hardwired proxy credentials