Enabling support for an API Application name

This commit is enabling the CirconusAPI.appname method as read from the circonusapirc config file, or passed in via the -a command line argument.

**NOTE:** This fix does not currently work with the version of [circonusapi as installed through pip](https://pypi.python.org/pypi/circonusapi/0.1.4). The version of circonusapi uploaded to the Pypi is slightly out of date with what's in [master](https://github.com/circonus-labs/python-circonusapi), specifically missing ` "X-Circonus-App-Name": self.appname,`.