* Split "matrix-constructors.rkt" into three parts:
* "matrix-constructors.rkt"
* "matrix-conversion.rkt"
* "matrix-syntax.rkt"
* Made `matrix-map' automatically inline (it's dirt simple)
* Renamed a few things, changed some type signatures
* Fixed error in `matrix-dot' caught by testing (it was broadcasting)
* Rewrote matrix comprehensions in terms of array comprehensions
* Removed `in-column' and `in-row' (can use `in-array', `matrix-col' and
`matrix-row')
* Tons of new rackunit tests: only "matrix-2d.rkt" and
"matrix-operations.rkt" are left (though the latter is large)
