Install: <module>_installer::install() is called, any necessary tables
are created.
Activate: <module>_installer::activate() is called. Module
controllers are routable, helpers are accessible, etc. The module is
in use.
Deactivate: <module>_installer::deactivate() is called. Module code
is not accessible or routable. Module is *not* in use, but its tables
are still around.
Uninstall: <module>_installer::uninstall() is called. Module is
completely removed from the database.
Admin > Modules will install and activate modules, but will only
deactivate (will NOT uninstall modules).
File_Structure_Test to make sure we don't regress.
According to the PHP docs, the "public" keyword is implied on static
functions, so remove it. Also, require private static functions to
start with an _.
http://php.net/manual/en/language.oop5.visibility.php
1) they now have their own matching severity constants
2) they both have convenience functions success(), info(), warning() and error()
3) they both have severity_class()
