Add option "ignoreExtends"

This change will add the option "ignoreExtends".

When this option is set to a array of jade files, these files will be ignored, when they are extended.

This way you can use layout files server-side, but don't use them client-side, because you only want the important part of the template there, e.g. to inject it with JS.

Example:
--------
*views/layout.jade*

    doctype html
    html
        head
            title Test
        body
            h1 Test
            nav#main-nav
                li
                    a(href="fu.html") Fu
                li
                    a(href="bar.html") Bar
            
            #content
                block content
                
            footer#main-footer
                p © Example Inc. 2014 
    
*views/index.jade*
    
    extends layout.jade
    block content
        p Welcome to my wonderful jade-driven website.
        
*app.js*

    var templatizer = require("templatizer");
    templatizer(__dirname + "/views", __dirname + "/static/js/views.js", {ignoreExtends: ["layout.jade"]});
    
=> *static/js/views.js*
    
    // ...
    // index.jade compiled template
    templatizer["index"] = function tmpl_index() {
        return "<p>Welcome to my wonderful jade-driven website.</p>";
    };

    // layout.jade compiled template
    templatizer["layout"] = function tmpl_layout() {
        return '<!DOCTYPE html><html><head><title>Test</title></head><body><h1>Test</h1><nav id="main-nav"><li><a href="fu.html">Fu</a></li><li><a href="bar.html">Bar</a></li></nav><div id="content"></div><footer id="main-footer"><p>© Example Inc. 2014</p></footer></body></html>';
    };
    // ...
    
*static/js/views.js* without `ignoreExtends`: 

    // index.jade compiled template
    templatizer["index"] = function tmpl_index() {
        return '<!DOCTYPE html><html><head><title>Test</title></head><body><h1>Test</h1><nav id="main-nav"><li      ><a href="fu.html">Fu</a></li><li><a href="bar.html">Bar</a></li></nav><div id="content"><p>Welcome to my       wonderful jade-driven website.</p></div><footer id="main-footer"><p>© Example Inc. 2014</p></footer></body      ></html>';
    };

    // layout.jade compiled template
    templatizer["layout"] = function tmpl_layout() {
        return '<!DOCTYPE html><html><head><title>Test</title></head><body><h1>Test</h1><nav id="main-nav"><li><a href="fu.html">Fu</a></li><li><a href="bar.html">Bar</a></li></nav><div id="content"></div><footer id="main-footer"><p>© Example Inc. 2014</p></footer></body></html>';
    };