math.matrices.elimination: move to extra
math.matrices.extras: expand with esoteric, less-used and unfinished code from basis
- math.matrices and .extras receive more words, tests, and docs
- matrix has become a predicate class
- 94% of matrices words have complete docs
- 77% of matrices.extras words have complete docs
- much more consistent naming for constructors etc
- added missing words / features such as main-diagonal and anti-transpose
- optimizations
- lots of documentation
4350bcbfcd