Update README.md

adds UML diagram

cleans more throughly based on rubocop -DS and reek -U

cleans up

extracts coin class to improve coin manager

extracts coin manager class from vending machine

adds product name instance variable

fixes self etc.

adds first pass at make change feature

completes second feature

Merge branch 'master' of https://github.com/tansaku/vending-machine-kata

Initial commit

gets us started on the select product feature

adds product

completes the accept coins feature