[core] Math parser defines a bunch of new functions
im(), iM(), ia(), iv(), is(), ip(), ic(), xm(), xM(), ym(), yM(), zm(), zM(), cm() and
cM() which compute the minimum, maximum, average, variance, sum, product, median and min/max coordinates in a possibly dynamic-sized image (same as variables
im, iM, ia, iv, is, ip, ic, xm, xM, ym, yM, zm, zM, cm, cM but used when the image has a dynamic size, i.e. when function
resize() has been used in the expression).