Sequencer
A fast(?) fullscreen image-sequence player

--------------------------------------------------------------------------------
Demo:
    https://ertdfgcvb.xyz/p2/sm/play.html#2

--------------------------------------------------------------------------------
How to use:
    The minimum paramters are two filenames of an image sequence.
    The parser tries to figure out if there are leading zeroes:

    const s1 = Sequencer.make({
        from : 'pics/pig/DSC04701.JPG',
        to   : 'pics/pig/DSC04775.JPG',
    });

    ...or just a plain numerical sequence:

    const s2 = Sequencer.make({
        from : 'pics/dog/1.png',
        to   : 'pics/dog/100.png',
    });

    All options:

    const opts = {
        canvas           : null,        // a valid canvas element (will be created if null)
        from             : '1.jpg',     // first file of the sequence
        to               : '10.jpg',    // last file of the sequence
        step             : 1,           // increment: to load only even images use 2, etc.
        scaleMode        : 'cover',     // can be: auto, cover, contain as in CSS3,
        direction        : 'x',         // can be: x, -x, y, -y
                                        // and determines the pointer direction,
                                        // applies only if playMode is drag or hover
        playMode         : 'drag',      // can be: none, drag, hover, auto
        loop             : 'loop',      // can be: loop, pong, none
        interval         : 10,          // interval in milliseconds between each frame,
                                        // applies only if playMode is auto,
                                        // if set to zero tries to update at every frame event
        autoLoad         : 'all',       // can be: all, first, none,
                                        // if first or none is used the loading
                                        // needs to be triggered manually with load().
        fitFirstImage    : false,       // resizes the canvas to the size of
                                        // the first loaded image in the sequence
        showLoadedImages : false,       // show images while loading the sequence, 
                                        // may be jumpy because of async laoding <- not a typo
        dragAmount       : 10,          // distance (in pixels) to trigger nextImage(),
                                        // can be < 1, but must be > 0
        hiDPI            : true,        // use HDPI if present
        imageLoad        : function     // callback for each image load
        queueComplete    : function     // callback for queue complete
    };

--------------------------------------------------------------------------------
Changelog:
      2.1
    - update to ECMAScript 2015 (aka ES6)
    - script is now an ES6 module (may need transpiling for legacy support)
      and loaded as such in the examples

      2.0
    - multiple instances
    - better parser (automatic leading zeroes detection)
    - canvas only (2d)
    - incremental drag
    - removed default loader (a custom one can be implemented via callback)
    - cover frame

--------------------------------------------------------------------------------
Todo:
    - remove 'loop' option (merge with playMode)
    - transpiled version for ES5 support
    - area hovering 
    - accept an image array as parameter
    - accept a spritesheet as parameter
    - WebGL support
    - better touch support

--------------------------------------------------------------------------------
Author:
    Andreas Gysin
    @andreasgysin (twitter)