Move config loader into the OpenPhoto class.

This allows config files to be used everywhere, not just from the commandline.
Re-ordered README since credentials now apply to all access methods, not just CLI
Update tests to use config files

Uses 'test' by default
Can be overridden using OPENPHOTO_TEST_CONFIG env var
Update test README with config file details
Handle quoted config keys
Add config unit tests
Config unit test tweaks
Merge branch 'master' into class_config

Conflicts:
	openphoto/__init__.py
	openphoto/openphoto_http.py
	tests/test_base.py
Merge pull request #32 from sneakypete81/class_config

Allow config files to be used everywhere