Add @/at format to import helpers from template

[MadLittleMods]

This allows you to reference helpers directly inside the handlebars template. The @ format syntax is the same as the require-hbs plugin from Guy Bedford.

Format:

{{@helpers/myhelper}}
{{#@helpers/myblockhelper}}...{{/helpers/myblockhelper}}

Added path map option(helpersAtPathMap: {}) to map a module name (such as "helpers") to a complete path making it easier to reference helpers.

Also added documentation on this new @ format.

---

Example taken from added documenation to readme.md:

Example: inline @/at helpers

src/hello.handlebars

<p>Hello {{firstName}}</p>
<p>HELLO! {{@helpers/capitals.helper firstName}}</p>
{{#@helpers/noop.helper}}
    <p>A block helper that invokes the block as though no helper existed.</p>
{{/helpers/noop}}
{{> footer}}

src/js/hbs-helpers/capitals.helper.js

module.exports = function(str) {
    return str.toUpperCase();
}

src/js/hbs-helpers/noop.helper.js

module.exports = function(options) {
    return options.fn(this);
}

gulpfile.js

var gulp = require('gulp');
var handlebars = require('gulp-compile-handlebars');
var rename = require('gulp-rename');

gulp.task('default', function () {
    var templateData = {
        firstName: 'Kaanon'
    },
    options = {
        ignorePartials: true,
        partials : {
            footer : '<footer>the end</footer>'
        },
        helpersAtPathMap: {
            'helpers': './src/js/hbs-helpers/'
        },
    }

    return gulp.src('src/hello.handlebars')
        .pipe(handlebars(templateData, options))
        .pipe(rename('hello.html'))
        .pipe(gulp.dest('dist'));
});

dist/hello.html

<p>Hello Kaanon</p>
<p>HELLO! KAANON</p>
<p>A block helper that invokes the block as though no helper existed.</p>
<footer>the end</footer>

---

Currently, in the current master branch of this project, the only way to batch helpers is to do something like this:

var glob = require("glob");
var parsePath = require('parse-filepath');
var compileHandlebars = require('gulp-compile-handlebars');

//...
.pipe(compileHandlebars({/*context*/}, {
    helpers : (function() {
        var helpers = {};
        // Get a list of all the helpers in the folder
        var helperFiles = glob.sync("./src/js/hbs-helpers/*.js", {});
        helperFiles.forEach(function(filePath, index, array) {
            var pathParts = parsePath(filePath);
            try {
                helpers[pathParts.name] = require(filePath);
            } catch(e) {

            }
        });

        //console.log(helpers);
        return helpers;
    })()
}))