removed unused ctor

Merge pull request #16 from ckuhn203/cleanup

Added link to Greed Algorithm article

Fixed readme image link

Added state diagram

Added build note

Added some future improvement notes

Moved StateContext interface to its own file

Moved fakes to its own namespace

Removed unused usings

Removed console app. I'm just not going to get to it.

Merge pull request #15 from ckuhn203/exactchange

Added issue numbers to comment

Ternary operators are nice.

Use refund calculator to determine exact change state