Add UPC A and E support

[h3x4d3c1m4l]

This PR adds support for the two most commonly used UPC barcodes. As UPC A is very similar to EAN 13, it's code could make use of the existing EAN 13 support ("Don't Repeat Yourself") but I decided to implement it as a separate symbology for the following reasons:

• Using the existing EAN 13 code could make the UPC A encoder throw exceptions which are specific to EAN 13 (this could confuse both developers and end users)
• The UPC A encoding scheme is a lot simpler than the EAN 13 encoding scheme, any bugs in the EAN 13 implementation are ruled out this way and I think the code is more clear this way (less cyclomatic complexity, UpcAEncoder code easy to follow)

Let me know your thoughts on this, I can of course adapt the code to use the existing EAN 13 implementation :)

[huysentruitw]

Thank you for this PR, I totally forgot about it 😳