Update reduction machinery for 0.7

[simonbyrne]

The promotion machinery for reduction in sum/prod was changed in JuliaLang/julia#25051. This updates the use.

[ararslan]

Tab here

[codecov-io]

Codecov Report

Merging #100 into master will decrease coverage by 1.88%.
The diff coverage is 60%.

@@            Coverage Diff             @@
##           master     #100      +/-   ##
==========================================
- Coverage   93.33%   91.44%   -1.89%     
==========================================
  Files           4        4              
  Lines         180      187       +7     
==========================================
+ Hits          168      171       +3     
- Misses         12       16       +4

Impacted Files	Coverage Δ
src/fixed.jl	100% <100%> (ø)	⬆️
src/normed.jl	97.67% <100%> (+0.02%)	⬆️
src/FixedPointNumbers.jl	90.27% <50%> (-5.25%)	⬇️

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[andreasnoack]

I've defined a few methods to resolve some ambiguities and then I've marked a few printing methods as broken to get this one ready. There are still some ambiguities as reported in #101 but I think we should merge this as is and then resolve the ambiguities later since this is blocking work other packages.

[timholy]

Thanks folks!