Remove outdated size tweak from performance tips section of manual
fix #7564

this is a combination of convert(Rational{T},x) not returning the
correct type, and the lack of a type check in codegen for new().
fix gemv! and gemm! in empty cases. fixes #7571

should always mutate, not sometimes return a new array
Print evaluated LHS and RHS in comparison tests.
Adds a resultexpr field to Success and Failure.