fpspreadsheet: Fix writing non-printable characters writing to xml-like formats (xlsx, ods, wikitable). Add test case to error tests. Improve syntaxhighlighter for wikitablemaker demo (still not perfect).

git-svn-id: http://svn.code.sf.net/p/lazarus-ccr/svn@3611 8e941d3f-bd1b-0410-a28a-d453659cc2b4