DRY
Add space needed between colon and first argument.
Change indentation to match last commit.
Add .is_imaginary method.
Change .is_real implementation to match other .is_* boolean methods.
Document and reformat .is_* bool methods.
Add tests for .is_* bool methods.
Add private utility sub sum-of-squares().
Add method .squarednorm, named as in p5-M::Q. To be renamed later.
Trim trailing whitespace.