Simplify the QI every time from the constructor

This avoids qiRecip not working due to a non-square-free value in the
square root term. Alas, it makes constructing a QI very slow.
Add qiModify
Add constants qiZero, qiOne
qiIsZero: Comment, INLINE
Avoid Rational math and the qi constructor, use qiModify
INLINE qiToFloat
Add Integer variants qiAddI, qiSubI, qiMulI, qiDivI
Make the speed of the qiToCF/cfToQI test reasonable