SAA1064 and Seven Segment display APIs

Here is my first attempt at the SAA1064 and seven segment display APIs. I've attempted to copy the style of the existing chip apis as much as possible, but have probably introduced some duplication.

I haven't implemented display for all the letters we need (notably 'M' and 'K').

There are 2 examples in the example folder that show how the apis should be used. The tests should also help to explain the various options of the apis.

I've built 2 types of api on the SAA1064, one allowing digits to be configured, and one that allows the individual pins to be set.

I've only tested against a 2 digit display too.