issue_5: 'INSERT COIN' is now the initial display
issue_5: Reject invalid input
issue_5: Reject invalid input
Revert "issue_5: Reject invalid input"

This reverts commit 8de9aa190c77c9b1349438bad8a94c59d5353c14.
Revert "Revert "issue_5: Reject invalid input""

This reverts commit 1d4a10e7c386d3a4577f5cfa136e87366480afcc.
issue_5: Added handling of quarter
issue_5: Added handling of dime and nickel
issue_5: Added identification of coins
issue_5: Can handle slugs of any kind now.
issue_5: Refactored the handling of legal tender so that we have less duplication
Merge pull request #6 from robkinyon/issue_5

Issue 5