Added sudo and script execution checks.

Install exits before do any operation if root access is not granted (sudo fail).
Also, if a command fails (set -e), script ends to avoid bad installation.
Then, issue could be detected and fixed. But a manual rollback is required.
-- End commit --

Hello Jay,
This is my first pull request, so excuse me if something is wrong (including this text).
The request only include a simple "sudo true" (success if $USER belongs to sudo group)
And a stop on error (set -e), that could be pretty useful when there are a problem, commonly with a package.
PS: thanks for the easy installation method.