Merge pull request #203 from bvssvni/master

Minor improvements to `Event`, `Key` and `Button`
Wrote "Introduction"
Updated "Introduction"
Added 3 first steps to get started
Improved "Getting started", added "How to get help"
Fixed gramatical error
Update tutorial.md
Added "Piston documentation"
Update tutorial.md
Update tutorial.md
Removed constructor for `GameWindowSettings`
Merge branch 'master' of https://github.com/PistonDevelopers/piston
Let examples compiled
Merge pull request #208 from Coeuvre/master

Removed constructor for `GameWindowSettings`
Started working on `GameIterator`