New package: gtk-doc (#15768)

* [gtk-doc] created template

* [gtk-doc] using custom url to standardize on dotted version

* [gtk-doc] added description and homepage

* [gtk-doc] added dependencies and added pdf variant

* [gtk-doc] commented out pdf variant

* [gtk-doc] cleaned up leftover fixmes

* [gtk-doc] flake8

* [gtk-doc] readded url

* [gtk-doc] python packages are build and run dependencies

var/spack/repos/builtin/packages/gtk-doc/package.py

+# Copyright 2013-2019 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack import *
+
+
+class GtkDoc(AutotoolsPackage):
+    """GtkDoc is a tool used to extract API documentation from
+    C-code like Doxygen, but handles documentation of GObject
+    (including signals and properties) that makes it very
+    suitable for GTK+ apps and libraries. It uses docbook for
+    intermediate files and can produce html by default and
+    pdf/man-pages with some extra work."""
+
+    homepage = "https://wiki.gnome.org/DocumentationProject/GtkDoc"
+    url = 'https://gitlab.gnome.org/GNOME/gtk-doc/-/archive/GTK_DOC_1_32/gtk-doc-GTK_DOC_1_32.tar.gz'
+
+    version('1.32', sha256='0890c1f00d4817279be51602e67c4805daf264092adc58f9c04338566e8225ba')
+
+    # Commented out until package dblatex has been created
+    # variant('pdf', default=False, description='Adds PDF support')
+
+    depends_on('autoconf', type='build')
+    depends_on('automake', type='build')
+    depends_on('libtool',  type='build')
+    depends_on('m4',       type='build')
+    depends_on('pkgconfig', type='build')
+
+    depends_on('python@3.2:', type=('build', 'run'))
+    depends_on('py-pygments', type=('build', 'run'))
+    depends_on('libxslt')
+    depends_on('libxml2')
+    depends_on('docbook-xsl')
+    # depends_on('dblatex', when='+pdf')
+
+    def url_for_version(self, version):
+        """Handle gnome's version-based custom URLs."""
+        url = 'https://gitlab.gnome.org/GNOME/gtk-doc/-/archive/GTK_DOC_{0}/gtk-doc-GTK_DOC_{0}.tar.gz'
+        return url.format(version.underscored)