Fixed compute_rank to take const vec by reference
Constified a temporary variable
to_upper_echelon_mut now exists, instead of cost overloading
More _mut for upper echelon
Fix basis now computes the rank of the sub-space matrix
Remove constrainst from outputs
Added output on failure in fix_basis
Grew this->outputs to the number of names
Fixed negate vs setting high bit error
Fixed tests

Dotqc was broken a bit ago by changes to output.
I don't really know what it ought to be, but I think it works.
Fixed demos to always include '.o ...'