PhpMyCodeGenerator 2.4.0 Released

This release adds/improves some instructions:
- Add two instructions TRACE_START and TRACE_STOP for program trace/debug purpose.
- Add an instruction ECHO_SHEET for displaying array values for debug purpose.
- Add another comment instruction C, as it is more convenient to use a short name to mark a comment.
- Add an instruction XML_TO_STRING for dumping a XML string for a XML node, with the example script "script - XML_FROM_CELL_ARRAY" updated to make use of the instruction to format output.
- Add an instruction ARRAY_MERGE_VALUE, which works similar to ARRAY_MERGE, but will evaluate the cell values.
- Improve the instruction XML_FROM_CELL_ARRAY, so that a cell array can be nested inside another cell array, with the example script "script - XML_FROM_CELL_ARRAY" updated to show how to use the feature.
- Improve the instruction XML_XPATH, so that it can work on DOMNode.