add helpers from config to locals passed to template

[jimlambie]

Include a config setting for helpers, pointing to a directory containing helper files. Each .js helper file will be added as a property to a helperFunctions object which will be merged with locals before passing them to the template renderer.

Config

  engines: {
    pug: {
      paths: {
        helpers: 'test/workspace/helpers'
      }
    }
  }

Directory structure

helpers/
|_ trim.js

Becomes...

{
  trim: [Function]
}

Usage

h1= trim(product.name)

[eduardoboucas]

Super!

[hydroes]

Looks good, seems like it will work straight out of the box once merged

[jimlambie]

@hydroes Are you ready to try it out? Should be easy enough to install directly from the branch to prove it'll do what we expect it to