Makes public UDTDefinition's constructor

Makes able to create an instance of UDTValue with the knowledge of the structure of the User Defined Type.

Example
-
	CREATE TYPE IF NOT EXISTS my_type ( bla ascii, val int);
	CREATE TABLE IF NOT EXISTS udt_table (key uuid, udt my_type, PRIMARY KEY (key));
Usually, we do ;

	INSERT INTO udt_table (key, udt) VALUES  (?, { bla : ?, val : ? });
But it would also allow from the Java driver (the second parameter is an instance of UDTValue) ;

	INSERT INTO udt_table (key, udt) VALUES  (?, ?);