Add functionality for quaternion algebras

[thofma]

• add is_split_with_zero_divisor
• add documentation

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 76.45%. Comparing base (69b7e7f) to head (6692cc8).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
src/QuadForm/Quad/Spaces.jl	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1810      +/-   ##
==========================================
+ Coverage   76.40%   76.45%   +0.04%     
==========================================
  Files         362      362              
  Lines      114917   114943      +26     
==========================================
+ Hits        87800    87877      +77     
+ Misses      27117    27066      -51     

Files with missing lines	Coverage Δ
src/AlgAss/AlgQuat.jl	92.95% <100.00%> (+6.82%)	⬆️
src/AlgAss/Elem.jl	88.18% <100.00%> (-0.30%)	⬇️
src/QuadForm/Quad/Spaces.jl	80.58% <0.00%> (-0.16%)	⬇️

... and 24 files with indirect coverage changes

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