Added Sheet class for the XLSX reader that exposes basic sheet info, such as name or ID.
When retrieving the sheet data XML, added extra XML parsing to retrieve sheet data.
Added test
Fixes#3:
The sheetN.xml files location is dynamically retrieved when parsing
[Content_Types].xml. In this file, the location is like "/xl/worksheets/sheet1.xml".
Because the zip stream wrapper expects the zip entry name to be like
"xl/worksheets/sheet1/xml" (without the first "/"), this first "/"
needs to be trimmed. It was trimmed using:
ltrim($this->dataXmlFilePath, DIRECTORY_SEPARATOR);
which obvisously does not work on Windows platform where DIRECTORY_SEPARATOR is "\".
Replacing DIRECTORY_SEPARATOR by '/' solves this issue.
Escaped line feed characters in shared strings before processing them.
This makes every string remain on one single line and therefore allow
fast retrieval
Replaced usages of "\n" by PHP_EOL
Added test for multiline strings
