defaultValue - set default value for optional arguments

Assigns default value to funtion optional input variable

DEFAULTVALUE Assigns default value to funtion input variable
DEFAULTVALUE ('NAME',VAL) check if variable NAME doesn't exist or
is empty. If this is the case, it assigns it the value VAL.
DEFAULTVALUE ('NAME',VAL,EMPTYVAL) assigns value VAL to variable
NAME if it doesn't exists or value EMPTYVAL if it's empty.
NOTE: The variable value IS NOT the function output. The function must
be called without output

Example:
function c=sumab(a,b)
% This function can be called either with one or two input arguments
narginchk(1,2)
defaultValue('b',1)
c=a+b;

By Luca Amerio
[e-mail]
27/01/2016