* Consolidated Gauss and Gauss-Jordan elimination
* Fixed Gaussian elimination to return all indexes for pivotless columns,
not just those < m
* Consolidated `matrix-row-echelon' and `matrix-reduced-row-echelon'
* Specialized row reduction for determinants; removed option to not do
partial pivoting (it's never necessary otherwise)
* Added `matrix-invertible?'
* Removed `matrix-solve-many'; now `matrix-solve' solves for multiple
columns
* Gave `matrix-inverse' and `matrix-solve' optional failure thunk arguments
* Made some functions that return multiple columns return arrays instead
(i.e. `matrix-column-space')
* Added more tests
1aebd171c5