Added Conversational Git book.
Added Data-Oriented design free eBook
Merge pull request #286 from ridelub/master

Update free-programming-books.md
Revert "Added Data-Oriented design free eBook"

This reverts commit dd0b69d071358d8ad72b7c53563972e9d970ed47.
Added DOD free ebook (without changing the WHOLE file)
Merge pull request #291 from Sirithang/master

Added Data-Oriented design free eBook