Relax requirements on printing for BigFloat

[oxinabox]

BigFloat length control works badly, we might need a new algorithm.
Either here or in julia
20 is still much shorter than usual.
Normlly BigFloats are >80 characters

[codecov-commenter]

Codecov Report

Merging #191 (063e797) into master (0f6e29a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #191   +/-   ##
=======================================
  Coverage   90.94%   90.94%           
=======================================
  Files          11       11           
  Lines         287      287           
=======================================
  Hits          261      261           
  Misses         26       26           

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