[WP 34S] Enhanced Y register display: fractions, bugfixes etc.

[Bit]

I've committed the following changes to SVN:
- enhanced Y register display
- optimization to use fewer iterations when calculating how many digits of the Y register can be displayed
- numeric contrast display

I've updated the compiled binary in post #13 in this thread. It has the following additional patches applied:
- optimized (fewer) display updates as explained in post #25, point 3 and post #34, point 1
- code size reduction as explained in post #34, point 2
I'm planning to commit these changes to SVN after some more testing has been done.