fails:Float#angle returns NaN if NaN
fails:Float#angle returns self if NaN
fails:Float#angle returns 0 if positive
fails:Float#angle returns 0 if +0.0
fails:Float#angle returns 0 if +Infinity
fails:Float#angle returns Pi if negative
fails:Float#angle returns Pi if -0.0
fails:Float#angle returns Pi if -Infinity
