Import include_absolute.rb

Previously this was included from a submodule, but requires updating in
order to update to jekyll 4.0.0.

.gitmodules

@@ -4,6 +4,3 @@
 [submodule "dependencies/pygments-high-contrast-stylesheets"]
 	path = dependencies/pygments-high-contrast-stylesheets
 	url = https://github.com/mpchadwick/pygments-high-contrast-stylesheets.git
-[submodule "dependencies/jekyll-include-absolute-plugin"]
-	path = dependencies/jekyll-include-absolute-plugin
-	url = https://github.com/tnhu/jekyll-include-absolute-plugin.git

_plugins/include_absolute.rb

@@ -1 +0,0 @@
-../dependencies/jekyll-include-absolute-plugin/include_absolute.rb

_plugins/include_absolute.rb

@@ -0,0 +1,84 @@
+# Copyright 2019 Tan Nhu, Maarten Brakkee
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+# plugin imported from https://github.com/tnhu/jekyll-include-absolute-plugin
+
+module Jekyll
+  class IncludeTagError < StandardError
+    attr_accessor :path
+
+    def initialize(msg, path)
+      super(msg)
+      @path = path
+    end
+  end
+
+  class IncludeAbsoluteTag < Liquid::Tag
+    VARIABLE_SYNTAX = %r!
+        (?<variable>[^{]*(\{\{\s*[\w\-\.]+\s*(\|.*)?\}\}[^\s{}]*)+)
+        (?<params>.*)
+      !x
+
+    def initialize(tag_name, markup, tokens)
+      super
+
+      @file = markup.strip
+    end
+
+    # Render the variable if required (@see https://goo.gl/N5sMV3)
+    def render_variable(context)
+      if @file.match(VARIABLE_SYNTAX)
+        partial = context.registers[:site]
+          .liquid_renderer
+          .file("(variable)")
+          .parse(@file)
+        partial.render!(context)
+      end
+    end
+
+    def render(context)
+      file  = render_variable(context) || @file
+      source = File.expand_path(context.registers[:site].config['source']).freeze
+      path   = File.join(source, file)
+
+      begin
+        partial = Liquid::Template.parse(read_file(path, context))
+
+        context.stack do
+          context['include'] = parse_params(context) if @params
+          partial.render!(context)
+        end
+      rescue => e
+        raise IncludeTagError.new e.message, path
+      end
+    end
+
+    def read_file(file, context)
+      File.read(file, file_read_opts(context))
+    end
+
+    def file_read_opts(context)
+      context.registers[:site].file_read_opts
+    end
+  end
+end
+
+Liquid::Template.register_tag('include_absolute', Jekyll::IncludeAbsoluteTag)

dependencies/jekyll-include-absolute-plugin

@@ -1 +0,0 @@
-Subproject commit 1ea7dc0de623dd20707a3ac2cdabc285622c263a