Add ability to use functions as control sources.

[KurtLoeffler]

This change allows functions to be specified in the controls section of the initialization config. This allows complex composite controls to be declared.

It also includes a change that allows negative values from those functions to be handled meaningfully.

Example

input = baton.new {
    controls = {
        left = {'key:left', 'key:a', 'axis:leftx-', 'button:dpleft'},
        right = {'key:right', 'key:d', 'axis:leftx+', 'button:dpright'},
        horizontal = function(input)
            --returns -1 to 1
            return input:get("right")-input:get("left")
        end,

        up = {'key:up', 'key:w', 'axis:lefty-', 'button:dpup'},
        down = {'key:down', 'key:s', 'axis:lefty+', 'button:dpdown'},
        vertical = function(input)
            --returns -1 to 1
            return input:get("down")-input:get("up")
        end,
        
        alt = {'key:lalt', 'key:ralt'},
        enter = {'key:kpenter', 'key:return'},
        toggleFullscreen = function(input)
            return input:down("alt") and input:pressed("enter")
        end
    }
}

function love.update(deltaTime)
    input:update()
    
    print(tostring(input:get("horizontal"))..", "..tostring(input:get("vertical")))

    if input:pressed("toggleFullscreen") then
        love.window.setFullscreen(not love.window.getFullscreen(), "desktop")
    end
end

[tesselode]

Apparently I forgot to look at this in 2019 and haven't checked this repo since...

I can definitely see the utility for defining composite buttons, but I don't understand why you would want controls to return negative numbers. Your example shows separate horizontal and vertical controls; wouldn't those be better handled by pairs?

@KurtLoeffler sorry for the incredibly late reply, is this even relevant to your life anymore?