Support module directories with index.js

[albertogasparin]

trafficstars

If a folder contains index.js, then we add the folder name as an available namespace in the plugin cache. Moreover, we try to handle different styles for dir names (lowercase, kebab-case and snakeCase).

This should be a nice step forward to make this plugin a generic solution to reduce imports and improve tree shaking. Closes #166

[AndersDJohnson]

@albertogasparin Do you mean kebab-case not kebabCase?

[danny-andrews]

This is siiiiiick. Any updates?

[albertogasparin]

@AndersDJohnson Those where the names of lodash methods I've used to match folder naming. But I've made it more clear.

[pr0da]

Is there any plan to merge this PR? Do you need any help?