User functions are declared as in ANSI C.  The data types available for
the function type are: void, matrix, vector, string, int, double.
These data types, except for void, are also available for declaring arguments
and local variables.  Additionally, declarations of local variables may
specify a storage class of extern, static, or auto (the default is auto) and
an initialization.  The default data type of arguments is matrix.  Functions
must be declared before they are used in the definitions of other functions.

Examples:	void f(double x);	/* just declares f */

		int g( matrix a, int m, n)	/* defines g */
		{
		    matrix x; int i, j;
		    ...
		}

Arguments declared as int or double are passed by value.  Arguments declared
as matrix, vector, or string are passed by address.  Functions declared as
int or double return a value.  Functions declared as matrix, vector, or string
can return a variable or a value.  Declared types do not affect the type of
data a variable can hold.  int a = [1.0 2.0 3.0] is legal but not recommended.