Add support for Office 365 files

[elCorsaiR]

Office 365 generates documents which may has no word/document.xml, but a word/document2.xml (and so on). If you try to process such document with current version of docx_replace you'll get Errno::ENOENT: No such file or directory - word/document.xml To resolve this issue I've made changes to get document file path from [Content_Types].xml