updated version allows better object and function handling

[polyrhythmatic]

@tambien and I spent some time working on this, and we came up with this solution. Hoping this works as a resolution to #815

Yotam also had the idea of using a function/token request system, and this is basically what he's implemented here. At the end of "p5.Tone.js", the buffer load function is rewritten and a registered function is instantiated and then called at the end of the async call. p5 can use this function to add it's increment/decrement function.

    Tone.registeredPreload = function(callback){
        return function(){
            callback();
        }
    };

    //overwrite load function
    Tone.Buffer.load = function (url, callback) {
        var handle = Tone.registeredPreload();
        var request = new XMLHttpRequest();
        request.open('GET', url, true);
        request.responseType = 'arraybuffer';
        // decode asynchronously
        request.onload = function () {
            Tone.context.decodeAudioData(request.response, function (buff) {
                if (!buff) {
                    throw new Error('could not decode audio data:' + url);
                }
                callback(buff);
                handle();
            });
        };
        //send the request
        request.send();
        return request;
    };

    p5.prototype.registerPreloadMethod("registeredPreload", Tone);

[polyrhythmatic]

@lmccart just wondering if you have any comments!

[lmccart]

this is great @polyrhythmatic! I will review as soon as I have a little time, hopefully later today.

[lmccart]

this looks good @polyrhythmatic thank you both for looking into this and cleaning up the preload function in p5.js.

[polyrhythmatic]

Thanks @lmccart ! Willing to continue working on this, perhaps there are other libraries that we want to integrate and could pose other issues.

[lmccart]

yeah, i think if you could add the info and example from tone.js to the wiki, that'd be very helpful.
https://github.com/processing/p5.js/wiki/Libraries#use-registerpreloadmethod-to-register-names-of-methods-with-p5-that-may-be-called-in-preload