All modules now expose their actions as public static constants
Issues: The menu module no longer closes when an item is clicked (before
it would intercept any executed command and look if it matches one of
its exec commands)
Before, if the command produced no output, the `m_output` field would
not have been overwritten and the old output was displayed.
But since this is an explicit trigger of the hook, the user would expect
the output to be updated to whatever the script produces (even if that
is nothing).
Ref: https://www.reddit.com/r/Polybar/comments/e9a8ww
Add a new module that allow users to configure hooks
on received ipc messages. The hook will execute the defined
shell script and the output of the script will be used
as the module content.
Ref #84
