Avoid greedy apos entity replacement in attributes

[gitusa]

When using a single quotation mark (') in an attribute value it'll be replaced to "'", e.g. myattribute="attribute's value" will be saved as myattribute="attribute&pos; value".

This replacement isn't necessary here: Microsoft says "In cases where the character might cause the XML parser to misinterpret the document structure, use the entity instead of typing the character" (https://msdn.microsoft.com/en-us/library/ms256190(v=vs.110).aspx)

As every attribute's value is enclosed with double quotation marks (and no single quotation marks are used for enclosing an attribute's value by tinyxml2) there is no concern of misinterpretation and a replacement shouldn't be made in order to keep the original xml source value.