Functions istext iscelltext

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));