Merge pull request #1 from ajp8164/master

updated readme file
Merge pull request #2 from ajp8164/master

Added test project and solution file.
Refactored InvoiceParams class with properties. Changed KeyValuePair to Dictionary and other minor changes.
Refactored invoice to use properties, renamed a method, fixed tests to work with changes
Merge pull request #3 from unChaz/feature/refactor

Feature/refactor