Various changes; see description

• Changes to Z#: & defined as 2$. The default file is not initially deleted. If the file exists, this function overwrites it by default
• Corrected a bug in Zt that produced an error for numeric input when the pattern to be replaced was at the end of string (for example, [1 2 3 1 2][1 2]0Zt gave an error)
• Corrected a bug in Octave's str2num
• Extended Zj with two-output version (secondary default): gives real and imaginary parts
• X= (isequal) now works for 0 or 1 inputs too. & corresponds to N$
• Extended U with second output indicating succcess of the conversion
• Included "power" in the description of W for easier search. Thanks to @DJMcMayhem