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

2 files changed, 10 insertions, 3 deletions

diff --git a/media/mediaType.go b/media/mediaType.go
index 01a6b9582..434672c43 100644
--- a/media/mediaType.go
+++ b/media/mediaType.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.
@@ -45,6 +45,7 @@ type Type struct {
 
 	Delimiter string `json:"delimiter"` // e.g. "."
 
+	// TODO(bep) make this a string to make it hashable + method
 	Suffixes []string `json:"suffixes"`
 
 	// Set when doing lookup by suffix.
@@ -138,6 +139,10 @@ var (
 	TOMLType       = Type{MainType: "application", SubType: "toml", Suffixes: []string{"toml"}, Delimiter: defaultDelimiter}
 	YAMLType       = Type{MainType: "application", SubType: "yaml", Suffixes: []string{"yaml", "yml"}, Delimiter: defaultDelimiter}
 
+	// Common image types
+	PNGType = Type{MainType: "image", SubType: "png", Suffixes: []string{"png"}, Delimiter: defaultDelimiter}
+	JPGType = Type{MainType: "image", SubType: "jpg", Suffixes: []string{"jpg", "jpeg"}, Delimiter: defaultDelimiter}
+
 	OctetType = Type{MainType: "application", SubType: "octet-stream"}
 )
 
@@ -158,6 +163,8 @@ var DefaultTypes = Types{
 	OctetType,
 	YAMLType,
 	TOMLType,
+	PNGType,
+	JPGType,
 }
 
 func init() {
diff --git a/media/mediaType_test.go b/media/mediaType_test.go
index ea6499a14..e51f29b12 100644
--- a/media/mediaType_test.go
+++ b/media/mediaType_test.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.
@@ -52,7 +52,7 @@ func TestDefaultTypes(t *testing.T) {
 
 	}
 
-	require.Equal(t, 15, len(DefaultTypes))
+	require.Equal(t, 17, len(DefaultTypes))
 
 }