Support onBuildRead

[benquarmby]

Add support for the onBuildRead optimizer option. This would enable mutation of the raw text before it is wrapped in a module.

A use case would be to allow HTML minification, such as:

var path = require('path');
var htmlMinifier = require('html-minifier');

function onBuildRead(moduleName, filePath, contents) {
    console.log('Optimizing module "' + moduleName + '" using path:');
    console.log(filePath);

    var extension = path.extname(filePath).toLocaleLowerCase();

    if (extension === '.html') {
        contents = htmlMinifier.minify(contents, {
            collapseWhitespace: true
        });

        return contents;
    }

    return contents;
}