If no handler specified in `render`, detect it
Detect returns class by default, or instance if specified
Make fakefile a mock instead of an io object

Makes it possible to mutate attributes, e.g. the name,
for tests
Add detect method of ImageFileHandler
Add get_file_extension function
Let's keep our __init__ files empty
...except for core functions into top-level __init__.py

cos' I'm a hypocrite
More CONTRIBUTING docs
Move MFRException -> exceptions.py