Book update#3

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aanno wants to merge 4 commits intospajus:masterfrom

aanno:book-update

Commits on Jul 21, 2015

Fixes for working on ubuntu vivid. Converted mp3 to ogg (as gosu does NOT SUPPORT mp3 on linux).
aanno
committed

Commits on Jul 24, 2015

Added .gitignore
Paschwuerfler
committed

Commits on Aug 24, 2015

version update
Paschwuerfler
committed

Commits on Sep 4, 2015

update ruby and ruby gems
aanno
committed