Allow resolving modules from src directory

[joeldenning]

For example:

import 'src/thing.js'

{
 resolve: {
   alias: {
     src: path.resolve(process.cwd(), 'src')
  }
}

[eckdanny]

IMO: maybe best to just add to the docs site Custom Webpack Configuration section.

Benefits of not baking it in:

1. no surprises for peeps who don't like alias-ing
2. opportunity for peeps who go crazy with alias'ing to create as many as they want