Fix#3999. Fix#4000. Fix#4002. Several bug reports and feature requests for Xml Reader arrived practically simultaneously. They are all small and hit the same code modules, so I have bundled them together in one PR.
- `loadSpreadsheetFromString` might try to open a file with a falsy name (like '0'), which results in an exception with a misleading message (or a completely unexpected result if a file with that name exists). Code will still throw an exception, but the message will no longer be misleading, and no file I/O will be attempted.
- function `trySimpleXmlLoadString` is deprecated. It should never have been implemented with public visibility, and the fact that it was made the fix above a little more difficult than it would otherwise have been. It is replaced with a private equivalent.
- Style reader function `parseStyles` will now use a better namespace-aware method of reading its Xml data. Peculiarly, the Xml for the Style elements can either include or not a namespace prefix. This is probably because the global namespace and the styles namespace are the same. The existing prefix-based code does not recognize their equivalence, but the new namespace-based code does. Xml Reader continues to use prefix-based code in several other places.
- Border line styles with Weight omitted or equal to 0 have been treated as no border, but they should be treated as 'hair' thickness.
- Support for Zoom is added to Xml Reader.
- In support of the above, new properties (and getters and setters) zoomScalePageLayoutView and zoomScaleSheetLayoutView are added to Worksheet/SheetView. (As far as I can tell, Excel does not support Sheet Layout View for Xml spreadsheets).
- Support is added for those new properties in Xlsx Reader and Writer.
- Xls Reader and Writer seem to work okay without changes. There is one test where Xls shows a different value for one of the properties than Xml or Xlsx, but the spreadsheet looks okay and I don't see any practical consequences of the difference.
- PageBreak support is added to Xml Reader.
- Code for writing out Column Page Breaks in Xlsx Writer was wrong (and, unsurprisingly, untested). A one-line change fixes it, and tests are added.
oleibman