Bd/sparse gauss

[BD-00]

Structured Gaussian elimination to compute kernel over sparse matrices.
Currently divided into a field and a ring version, work still in progress.

[codecov]

Codecov Report

Attention: Patch coverage is 0.41754% with 477 lines in your changes missing coverage. Please review.

Project coverage is 75.52%. Comparing base (bdeaacb) to head (71796a1).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
src/Sparse/StructuredGauss.jl	0.00%	477 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1606      +/-   ##
==========================================
- Coverage   75.85%   75.52%   -0.34%     
==========================================
  Files         361      362       +1     
  Lines      113700   114176     +476     
==========================================
- Hits        86248    86231      -17     
- Misses      27452    27945     +493     

Files with missing lines	Coverage Δ
src/Sparse/Matrix.jl	71.46% <100.00%> (ø)
src/Sparse/StructuredGauss.jl	0.00% <0.00%> (ø)

... and 30 files with indirect coverage changes