Adding CONTRIBUTING.md. Using the new format for all the lists.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	free-programming-books-es.md
	free-programming-books-ru.md
	free-programming-interactive-tutorials-en.md
Merge branch 'master' of github.com:matysanchez/free-programming-books into matysanchez-master

Conflicts:
	free-programming-books-es.md
	free-programming-books-ru.md
	free-programming-books.md
	free-programming-interactive-tutorials-en.md