Functions istext iscelltext

Test for char or string variables; Test for cell array of char or string variables.

Most function now allow either char of string variables.
However missing are functions to test for either string or char,
and to test for a cell array containing only string or char values.

Two functions v=istext(x) and v=iscelltext(x) are included or
can be used inline as:

istext=@(x)isstring(x)|ischar(x);
iscelltext=@(x)all(cellfun(@(y)isstring(y)|ischar(y),x,'UniformOutput',1));