Autoload securely a project.el file when entering a project directory.

It uses projectile package. When entering a new project, load the project.el file at the root of the project. To make things safes, it check a project.el.sig GPG signature file and verify the file was signed by one of the =auto-load-project-trusted-gpg-key-fingerprint=.

(setq auto-load-project-trusted-gpg-key-fingerprints '("000011112222333344445555666677778888"))