Allow sections & snippets within subfolders

[westonganger]

Solves locomotivecms/engine#1313

[WIP] currently only works locally with wagon serve, deploying has issues which can be solved using encoding and decoding of the url.

[did]

thanks @westonganger! I think I can fix the deployment thing.

[did]

In order to avoid slug collisions, I suggest that the convention for the section slug should be <sub folder>--<filename of the section>.

Examples: global--header (sections/global/header.liquid), home--page_hero (sections/home/page_hero.liquid).

@westonganger what do you think?

[westonganger]

I would definitely prefer to refer to them via the path home/page_hero when calling it in the view.

However under the hood for the slug, I would propose the following (in order of preference)

• home::page_hero
• home:page_hero
• home--page_hero