Level 04 contains some testing fun.
Removed spurious yaml file from level03.
Update README.
Have noticed irritating snafu RE the app structure. Not built as a
library in other levels, will fix.
Level 03 updated with a bit more information, removed yaml-config due to other
issues. Added the configuration to the main and updated the relevant bits.
Not written up with comments or even very clean at the moment.
Trying to decide between exceptions and YAML or no exceptions but
manual parsing for JSON config file.
Or something else entirely...
