This document contains (hopefully) all you need to know about
the control_handler, and any other relevant input systems

The control system is designed to be simple but versatile,


    ----------------------------------------------------------------------------
                                basic information
    ----------------------------------------------------------------------------

    IMPORTANT: `on_use` and `on_secondary_use` are RESERVED indexes. They
    have different behaviors and function parameters. (see special actions)

    control action example:
        ------------------------------------------------------------------------
        (The default aim taken from gun_api.lua)
        aim = {
            conditions = {"RMB"},
            loop = false,
            timer = 0,
            func = function(active, interrupted, data, busy_list, handler)
                if active then
                    handler.control_bools.ads = not handler.control_bools.ads
                end
            end
        },
        ------------------------------------------------------------------------

    here's the breakdown:

        `conditions = {"RMB"}` is the list of conditions (see get_player_control
        in minetest's lua_api.txt) that need to be fufulled for the control to
        be activated

        `timer = 0` tells the handler that if condtions are met for 0 seconds
        that it is active.

        `loop = false` indicates the it only will call once if the key(s) are
        held for the the specified amount of time `timer = 0`. In short, this
        tells the handler to run the function one time instead of calling it
        in (as the name implies) a loop.

    additional properties:

        `call_before_timer = false` if true, then the handler calls the function
        while the timer is in progress, this is very useful if you want something
        like a reload animation, or maybe a bow with a cocking animation, etc.
        use the function parameters (as follows) for better information.

    ----------------------------------------------------------------------------
                          standard function parameters
    ----------------------------------------------------------------------------

    function parameters for normal actions (see special actions)

        `active` indicates wether conditions or timers were met/finished, the
        function can be called for reasons other then conditions being finished.
        use this to check if you actually want to do an action (such as firing)
        or finalizing reloads.

        `interrupted` indicates if conditions were no longer met while the timer
        was in progress. This cannot not be called with active as true.

        `data` is actually the Control_handler's table for the control action,
        it has `timer` which is the time left on the action and `held` which
        indicates if the keyboard and mouse conditions are met.

        `busy_list` is a list of other active actions, use this if you want to
        only act if

        `handler` is the Player_handler, this is guns4d's *everything* handler.
        to get the gun use `handler.gun`, to get the player use `handler.player`

    ----------------------------------------------------------------------------
                                special action
    ----------------------------------------------------------------------------

        The indexes `on_use` and `on_secondary_use` are reserved for calls from
        the default on_use and on_secondary_use of tools. By default, the on_use
        and on_secondary_use of the itemstring provided is overwritten to contain
        this call.

        set these as functions (with the following parameters) for on_use and
        on_secondary_use. It's not set in busy list by defaults, so if you
        wish (or otherwise need to) add a `self.busy_list.on_use = true` to it.
        note that the busy list is cleared each update by default.

        function parameters:
        `itemstack`, `handler`, `pointed_thing`
        see lua_api.txt for details on `itemstack` and `pointed_thing` and
        see "standard function parameters" for handler info.