Make Page an interface

The main motivation of this commit is to add a `page.Page` interface to replace the very file-oriented `hugolib.Page` struct.
This is all a preparation step for issue  #5074, "pages from other data sources".

But this also fixes a set of annoying limitations, especially related to custom output formats, and shortcodes.

Most notable changes:

* The inner content of shortcodes using the `{{%` as the outer-most delimiter will now be sent to the content renderer, e.g. Blackfriday.
  This means that any markdown will partake in the global ToC and footnote context etc.
* The Custom Output formats are now "fully virtualized". This removes many of the current limitations.
* The taxonomy list type now has a reference to the `Page` object.
  This improves the taxonomy template `.Title` situation and make common template constructs much simpler.

See #5074
Fixes #5763
Fixes #5758
Fixes #5090
Fixes #5204
Fixes #4695
Fixes #5607
Fixes #5707
Fixes #5719
Fixes #3113
Fixes #5706
Fixes #5767
Fixes #5723
Fixes #5769
Fixes #5770
Fixes #5771
Fixes #5759
Fixes #5776
Fixes #5777
Fixes #5778

1 files changed, 8 insertions, 7 deletions

diff --git a/hugolib/site_output.go b/hugolib/site_output.go
index 0a7513961..9fb236506 100644
--- a/hugolib/site_output.go
+++ b/hugolib/site_output.go
@@ -1,4 +1,4 @@
-// Copyright 2017-present The Hugo Authors. All rights reserved.
+// Copyright 2019 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -18,6 +18,7 @@ import (
 
 	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/output"
+	"github.com/gohugoio/hugo/resources/page"
 	"github.com/spf13/cast"
 )
 
@@ -28,11 +29,11 @@ func createDefaultOutputFormats(allFormats output.Formats, cfg config.Provider)
 	sitemapOut, _ := allFormats.GetByName(output.SitemapFormat.Name)
 
 	return map[string]output.Formats{
-		KindPage:         {htmlOut},
-		KindHome:         {htmlOut, rssOut},
-		KindSection:      {htmlOut, rssOut},
-		KindTaxonomy:     {htmlOut, rssOut},
-		KindTaxonomyTerm: {htmlOut, rssOut},
+		page.KindPage:         {htmlOut},
+		page.KindHome:         {htmlOut, rssOut},
+		page.KindSection:      {htmlOut, rssOut},
+		page.KindTaxonomy:     {htmlOut, rssOut},
+		page.KindTaxonomyTerm: {htmlOut, rssOut},
 		// Below are for conistency. They are currently not used during rendering.
 		kindRSS:       {rssOut},
 		kindSitemap:   {sitemapOut},
@@ -65,7 +66,7 @@ func createSiteOutputFormats(allFormats output.Formats, cfg config.Provider) (ma
 		for _, format := range vals {
 			f, found := allFormats.GetByName(format)
 			if !found {
-				return nil, fmt.Errorf("Failed to resolve output format %q from site config", format)
+				return nil, fmt.Errorf("failed to resolve output format %q from site config", format)
 			}
 			formats = append(formats, f)
 		}