Fix issue #92

The dolist form in the alert function receives an empty list. This solution adds a single element nil to the list so that the dolist executes the body at least once.

Additionally, the :persistent keyword is added to the base-info variable, because when it is not in the base-info, then it will not get passed to the final if form (i.e. when the user has not configured some alert or added a :style keyword to the alert call). Finally, the user can use the :icon keyword to set an icon, so that info is added to the alert docstring.

Currently, when using e.g. libnotify specifications for icons can be found in the Freedesktop Icon Naming Specification.