Move image stack to its own module
Move __init__ functions to submodules.

And rename functions so we don't have to alias imports.
Use explicit imports
Remove debugging statement
Remove unnecessary class
Remove unnecessary initialization
Refactor io doc building code
Factor out table formatting code.
Minor rename
Fix wrapping of plugin descriptions
Factor out config-file parsing for clarity
Add comment for clarification
Factor out url handling for unified file/url behavior
Add test that error gets raised when no plugin available
PEP8
Fix test so it doesn't have side-effects
Change InheritedConfig so a key is contained if a parent key is contained
Move tests to separate file.
Change plugin_store to use InheritedConfig
Use InheritedConfig for plugin_store