Functionality for alternative configuration files

I have implemented functionality for using alternative configuration files. This is necessary for interactive applications, because every user needs a separate configuration file. Also library directories must be world readable on Linux computers, disclosing the secret keys to every user of the system. 

The functionality has only been tested with the finding and shopping API, because most tests are broken. However I'm convinced that it works everywhere, because the changes are very simple. I have created test and example scripts for the functionality itself:
* `tests/test_alternative_config.py`
* `examples/example_alternative_config.py`

I have also modified the tests for the finding API (`tests/test_finding.py`). Now all test have meaningful argument values, and they pass on Ebay's production system.

If necessary I can distribute the changes into two pull requests: 
1. Modify tests for finding API.
2. Add functionality for alternative configuration files.