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

tpl/tplimpl/shortcodes_test.go

@@ -0,0 +1,94 @@
+// 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.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tplimpl
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestShortcodesTemplate(t *testing.T) {
+
+	t.Run("isShortcode", func(t *testing.T) {
+		assert := require.New(t)
+		assert.True(isShortcode("shortcodes/figures.html"))
+		assert.True(isShortcode("_internal/shortcodes/figures.html"))
+		assert.False(isShortcode("shortcodes\\figures.html"))
+		assert.False(isShortcode("myshortcodes"))
+
+	})
+
+	t.Run("variantsFromName", func(t *testing.T) {
+		assert := require.New(t)
+		assert.Equal([]string{"", "html", "html"}, templateVariants("figure.html"))
+		assert.Equal([]string{"no", "no", "html"}, templateVariants("figure.no.html"))
+		assert.Equal([]string{"no", "amp", "html"}, templateVariants("figure.no.amp.html"))
+		assert.Equal([]string{"amp", "amp", "html"}, templateVariants("figure.amp.html"))
+
+		name, variants := templateNameAndVariants("figure.html")
+		assert.Equal("figure", name)
+		assert.Equal([]string{"", "html", "html"}, variants)
+
+	})
+
+	t.Run("compareVariants", func(t *testing.T) {
+		assert := require.New(t)
+		var s *shortcodeTemplates
+
+		tests := []struct {
+			name     string
+			name1    string
+			name2    string
+			expected int
+		}{
+			{"Same suffix", "figure.html", "figure.html", 3},
+			{"Same suffix and output format", "figure.html.html", "figure.html.html", 3},
+			{"Same suffix, output format and language", "figure.no.html.html", "figure.no.html.html", 3},
+			{"No suffix", "figure", "figure", 3},
+			{"Different output format", "figure.amp.html", "figure.html.html", -1},
+			{"One with output format, one without", "figure.amp.html", "figure.html", -1},
+		}
+
+		for i, test := range tests {
+			w := s.compareVariants(templateVariants(test.name1), templateVariants(test.name2))
+			assert.Equal(test.expected, w, fmt.Sprintf("[%d] %s", i, test.name))
+		}
+
+	})
+
+	t.Run("indexOf", func(t *testing.T) {
+		assert := require.New(t)
+
+		s := &shortcodeTemplates{
+			variants: []shortcodeVariant{
+				shortcodeVariant{variants: []string{"a", "b", "c"}},
+				shortcodeVariant{variants: []string{"a", "b", "d"}},
+			},
+		}
+
+		assert.Equal(0, s.indexOf([]string{"a", "b", "c"}))
+		assert.Equal(1, s.indexOf([]string{"a", "b", "d"}))
+		assert.Equal(-1, s.indexOf([]string{"a", "b", "x"}))
+
+	})
+
+	t.Run("Template", func(t *testing.T) {
+		assert := require.New(t)
+
+		assert.True(true)
+
+	})
+}