Pagination support

[jesseleite]

Previously, we linked people to this gist, which was self-described as a temporary workaround:

We will likely introduce better native support for pagination at some point, but for now, this is an okay workaround that only requires a little code.

This PR adds intelligent pagination support by detecting where paginators are used in core (ie. the {{ collection }} tag with the paginate parameter), generating /articles/page/2 style urls for each page where necessary.

No extra setup or user config is required, unless the user wishes to customize the output url, which they can do like so...

• Configuring 'pagination_route' => '{url}/{page_name}/{page_number}' would result in /articles/page/2 (default)
• Configuring 'pagination_route' => '{url}/{page_name}-{page_number}' would result in /articles/page-2
• Configuring 'pagination_route' => '{url}/{page_name}{page_number}' would result in /articles/page2
• Configuring 'pagination_route' => '{url}/p/{page_number}' would result in /articles/p/2
• Configuring 'pagination_route' => '{url}/p{page_number}' would result in /articles/p2
• Configuring 'pagination_route' => '{url}/{page_number}' would result in /articles/2
• Configuring 'pagination_route' => '{url}{page_number}' would result in /articles2

This PR also respects multisite collection indexes, as well as collection tag per-page settings, filters, query scopes, pagination links, auto_links, etc.

Closes #10 Closes #63

[mbootsman]

Great! It works perfectly. Thanks a lot!!