Improving FIX mode

[Albert Chan]

I think in FIX mode, we are not supposed to see "E"

Scientific notation switch really signals FIX conversion failed.
(Either overflowed limited display or underflow to 0.000...)

https://github.com/c3d/DB48X-on-DM42/issues/412 Wrote:// Also, since DB48X can compute on 34 digits, and counting zeroes
// can be annoying, there is a separate setting for when to switch
// to scientific notation.

To count zeroes, I found that normalized mode is better: 0.1 ≤ |mantissa| < 1
see IEEE Standard for Floating Point Numbers, by V Rajaraman

12345000 --> 0.12345e+008 --> 8 digits integer part
0.0012345 --> 0.12345e-002 --> 2 0's after decimal point.