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, 6 insertions, 8 deletions

diff --git a/hugolib/gitinfo.go b/hugolib/gitinfo.go
index d356fcf07..6acc47d17 100644
--- a/hugolib/gitinfo.go
+++ b/hugolib/gitinfo.go
@@ -1,4 +1,4 @@
-// Copyright 2016-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.
@@ -19,6 +19,7 @@ import (
 
 	"github.com/bep/gitmap"
 	"github.com/gohugoio/hugo/config"
+	"github.com/gohugoio/hugo/resources/page"
 )
 
 type gitInfo struct {
@@ -26,15 +27,12 @@ type gitInfo struct {
 	repo       *gitmap.GitRepo
 }
 
-func (g *gitInfo) forPage(p *Page) (*gitmap.GitInfo, bool) {
-	if g == nil {
-		return nil, false
-	}
-
-	name := strings.TrimPrefix(filepath.ToSlash(p.Filename()), g.contentDir)
+func (g *gitInfo) forPage(p page.Page) *gitmap.GitInfo {
+	name := strings.TrimPrefix(filepath.ToSlash(p.File().Filename()), g.contentDir)
 	name = strings.TrimPrefix(name, "/")
 
-	return g.repo.Files[name], true
+	return g.repo.Files[name]
+
 }
 
 func newGitInfo(cfg config.Provider) (*gitInfo, error) {