SAA1064 and Seven Segment display APIs

Updated API based off conversations with Nat last Tuesday.

Deferred configuration to first data write to the chip. This means it's impossible to forget to configure the chip. 

Fixed a problem with padding on displaying strings of length less than the number of digits. For example, displaying '10' on a 4 digit display, used to show '10--' (where - signifies a blank digit). Now it shows '--10'.