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, 7 insertions, 4 deletions

diff --git a/helpers/general.go b/helpers/general.go
index 00caf1ecc..962b35bc6 100644
--- a/helpers/general.go
+++ b/helpers/general.go
@@ -1,4 +1,4 @@
-// Copyright 2015 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.
@@ -92,7 +92,7 @@ func GuessType(in string) string {
 		return "org"
 	}
 
-	return "unknown"
+	return ""
 }
 
 // FirstUpper returns a string with the first character as upper case.
@@ -325,12 +325,15 @@ func InitLoggers() {
 // The idea is two remove an item in two Hugo releases to give users and theme authors
 // plenty of time to fix their templates.
 func Deprecated(object, item, alternative string, err bool) {
+	if !strings.HasSuffix(alternative, ".") {
+		alternative += "."
+	}
+
 	if err {
 		DistinctErrorLog.Printf("%s's %s is deprecated and will be removed in Hugo %s. %s", object, item, hugo.CurrentVersion.Next().ReleaseVersion(), alternative)
 
 	} else {
-		// Make sure the users see this while avoiding build breakage. This will not lead to an os.Exit(-1)
-		DistinctFeedbackLog.Printf("WARNING: %s's %s is deprecated and will be removed in a future release. %s", object, item, alternative)
+		DistinctWarnLog.Printf("%s's %s is deprecated and will be removed in a future release. %s", object, item, alternative)
 	}
 }