Ecmwf-api-client

To replace existing behaviour where we fail silently and try the next available method of providing an API access key, ultimately falling back to anonymous access.

Also, updated the README to clean it up and make it clearer.

The library uses `print` statements by default for logging, but allows users to change that behavior by providing their own logging function when instantiating `ecmwfapi.ECMWFDataServer` and `ecmwfapi.ECMWFService`. That functionality was broken in the sense that it didn't apply to all the produced logging messages, and some of them still used `print`, instead of the user provided logging function, no matter what. The issue should now be solved.

Enable anonymous access.

Integrate some user pull requests to remove whitespace, fix spelling, and drop the use of `simplejson`.