Squashed 'libs/glfw/' content from commit e4d3f86

git-subtree-dir: libs/glfw
git-subtree-split: e4d3f860977baa314f022d7db5ed3420389ba372
Merge commit '4cd1317718bab1777b5a8f851b1b4304d4afbf56' as 'libs/glfw'
updated gitignore, build.sh and added clean.sh
Updated gitignore and build.sh