Edit in JSFiddle

var ghe = {
     apiBase: 'https://api.github.com'
    ,callbacks: {}
    ,library: {}
    ,rLeadSlash: /^\/+|\/+$/g
}

ghe.keygen = function(){
    return 'ghe_' + ~~(Math.random() * 100000);
}

ghe.jsonpCallback = function(key){
    return ghe.callbacks[key] = function(resp){
        var lib = ghe.library[key];

        console.log( 'retrieved library data', lib );
        console.log( 'response', resp );
    }
}

ghe.jsonp = function(fileUrl, cbName){
    var script = document.createElement('script');
    script.async = true;
    script.src = fileUrl + '?callback=' + cbName;
}

ghe.parseNode = function(el){
    
    var lines = el.getAttribute('data-ghlines')
        ,start
        ,end;
    
    if(lines && lines.indexOf('-') > -1){
        lines = lines.split('-');
        start = parseInt( lines[0], 10 );
        end = parseInt( lines[1], 10 );
    } else if( lines ){
        start = end = parseInt( lines, 10 );
    } else {
        start = end = -1;
    }

    return {
         path: el.getAttribute('data-ghpath')
        ,userrepo: el.getAttribute('data-ghuserrepo')
        ,lineBegin: start
        ,lineEnd: end
        ,el: el
    }
}

ghe.load = function(cfg){
    
    var key = ghe.keygen();
    
    if( cfg.nodeName ){
        cfg = ghe.parseNode(cfg);
    }
    
    ghe.jsonpCallback(key);
    ghe.library[key] = cfg;
    ghe.jsonp( 
        ghe.apiBase 
            + '/repos/' 
            + cfg.userrepo.replace(ghe.rLeadSlash, '') 
            + '/contents/' 
            + cfg.path.replace(ghe.rLeadSlash, '')
        ,key
    );
}

ghe.autorun = function(){
    var nodes;
  
    if( window.jQuery ){
        nodes = $('[data-ghpath]')  
    } else {
        nodes = document.querySelectorAll('[data-ghpath]');
    }
  
    for(var i = 0; i < nodes.length; i++){
        console.log(nodes[i]);
        ghe.load(nodes[i]);
    }
}

ghe.autorun();
console.log(ghe);
  
/*var css = document.createElement('link');
css.type = 'text/css';
css.ref = 'stylesheet';
css.href = 'https://gist.github.com/stylesheets/gist/embed.css';
css.media = 'screen';
document.getElementsByTagName('head')[0].appendChild(css);

var  container = document.createElement('div')
    ,url = 'https://api.github.com/repos/kirbysayshi/broad-phase-bng/contents/examples/bruteforce/orbit-01.js'
    ,req = new XMLHttpRequest();

container.className = 'gist';
document.getElementsByTagName('body')[0].appendChild(container);

req.open( 'GET', url, true );

req.onreadystatechange = function(){        
    var parsed, lines, filename, gist, pre;
    if(req.readyState === 4){
        parsed = JSON.parse( req.responseText );
        console.log(parsed);
        
        filename = url.split('/').pop();
        content = atob( parsed.content.replace(/\s/g, '') );
        lines = content.split('\n');
        lines = lines.map(function(l, i){
            return '<a id="#' + filename + '-' + i + '"></a>'
                + l.replace(/\t/g, '&nbsp;&nbsp;&nbsp;&nbsp;')
                    .replace(/^ +/g, '&nbsp;');
        });
        
        console.log( lines.join('\n') );
        
        gist = document.createElement('div');
        gist.className = 'gist-file';
        gist.innerHTML = lines.join('<br />');
        
        container.appendChild(gist);
        
    } else {
        console.log(arguments);
    }
}

req.send();*/

<div data-ghpath="examples/bruteforce/orbit-01.js" data-ghuserrepo="kirbysayshi/broad-phase-bng" data-ghlines="4-10" class="gist"></div>