Remove spam dependency

[bryo-han]

Matrix::solve can solve triangular systems/do forward and backward substitution. So, spam may not be needed as a dependency.

To work with Matrix::solve, the triangular matrix must be of a suitable class. pedigreeTools::getLInv returns class dtCMatrix, which is suitable. A matrix imported from MatrixMarket format has to be converted using as(myMat, "dtCMatrix"). Not sure whether a matrix in spam format can be converted w/o going through a dense matrix.

Performance of Matrix::solve compares well with spam both with simulated and Labrador data.

[bryo-han]

• Obvious, but check that results are the same (edited by GG)
• Remove dependency
• Update L inverse objects. Need to be dtCMatrix, not spam
• Update vignette

[gregorgorjanc]

These notes from today's meeting might be handy for this issue