Introduce snake case function incidence_matrix

[alexej-jordan]

IncidenceMatrix does not have snake case constructors. This PR fixes that, properly documents the available methods and adjusts existing (doc-)tests.

Solves #4033

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.59%. Comparing base (eaa8972) to head (a156c84).
Report is 4 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4245   +/-   ##
=======================================
  Coverage   84.59%   84.59%           
=======================================
  Files         631      631           
  Lines       85064    85085   +21     
=======================================
+ Hits        71960    71981   +21     
  Misses      13104    13104           

Files with missing lines	Coverage Δ
...erimental/Schemes/src/ToricBlowups/constructors.jl	89.83% <ø> (ø)
...ricVarieties/AlgebraicCycles/special_attributes.jl	100.00% <ø> (ø)
...ometry/ToricVarieties/CohomologyClasses/methods.jl	61.53% <ø> (ø)
...oricVarieties/NormalToricVarieties/constructors.jl	100.00% <ø> (ø)
...lyhedralGeometry/PolyhedralComplex/constructors.jl	95.45% <ø> (ø)
...PolyhedralGeometry/PolyhedralComplex/properties.jl	86.27% <ø> (ø)
...ometry/PolyhedralComplex/standard_constructions.jl	100.00% <ø> (ø)
...c/PolyhedralGeometry/PolyhedralFan/constructors.jl	88.63% <ø> (ø)
src/PolyhedralGeometry/PolyhedralFan/properties.jl	98.33% <ø> (ø)
...hedralGeometry/SubdivisionOfPoints/constructors.jl	79.16% <ø> (ø)
... and 7 more

... and 3 files with indirect coverage changes

[benlorenz]

Thanks, looks good in general, needs one run of the julia formatter.

But I think we should disallow the non-bool / non-0-1 matrix input.

[benlorenz]

Thinking about this again, we should keep the input in the book tests as they are to make sure it keeps working.