Add a way to override the app help printer

Fixes #64
Merge pull request #65 from tjarratt/custom-help-printer

Add a way to override the app help printer
Fixed typo in README
Merge pull request #67 from tenpeoplemeet/patch-1

Fixed typo in README
add tests for description output
fix whitespace
rollback inconsequential changes
Merge pull request #68 from bunnymatic/checking-that-description-works

Checking that description works