docs: Port the man pages from DocBook to reStructuredText

So they are consistent with the way we’re building man pages in other
projects, and because some people are allergic to XML.

This changes the build-time dependencies from `xsltproc` to `rst2man`,
and also takes the opportunity to change the `-Dman` Meson option from a
boolean to a feature (so you should use `-Dman-pages={enabled,disabled}`
now, rather than `-Dman={true,false}`).

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Helps: #3037

docs/reference/gio/glib-compile-schemas.rst

@@ -0,0 +1,83 @@
+.. _glib-compile-schemas(1):
+.. meta::
+   :copyright: Copyright 2010, 2011, 2012, 2015 Red Hat, Inc.
+   :copyright: Copyright 2012 Allison Karlitskaya
+   :copyright: Copyright 2016 Sam Thursfield
+   :license: LGPL-2.1-or-later
+..
+   This has to be duplicated from above to make it machine-readable by `reuse`:
+   SPDX-FileCopyrightText: 2010, 2011, 2012, 2015 Red Hat, Inc.
+   SPDX-FileCopyrightText: 2012 Allison Karlitskaya
+   SPDX-FileCopyrightText: 2016 Sam Thursfield
+   SPDX-License-Identifier: LGPL-2.1-or-later
+
+====================
+glib-compile-schemas
+====================
+
+-------------------------
+GSettings schema compiler
+-------------------------
+
+SYNOPSIS
+--------
+
+|  **glib-compile-schemas** [*OPTION*…] *DIRECTORY*
+
+DESCRIPTION
+-----------
+
+``glib-compile-schemas`` compiles all the GSettings XML schema files in
+``DIRECTORY`` into a binary file with the name ``gschemas.compiled`` that can be
+used by ``GSettings``. The XML schema files must have the filename extension
+``.gschema.xml``. For a detailed description of the XML file format, see the
+``GSettings`` documentation.
+
+At runtime, GSettings looks for schemas in the ``glib-2.0/schemas``
+subdirectories of all directories specified in the ``XDG_DATA_DIRS`` environment
+variable. The usual location to install schema files is
+``/usr/share/glib-2.0/schemas``.
+
+In addition to schema files, ``glib-compile-schemas`` reads ‘vendor override’
+files, which are key files that can override default values for keys in
+the schemas. The group names in the key files are the schema ID, and the
+values are written in serialized GVariant form.
+Vendor override files must have the filename extension
+``.gschema.override``.
+
+By convention, vendor override files begin with ``nn_`` where ``nn`` is a number
+from 00 to 99.  Higher numbered files have higher priority (e.g. if the same
+override is made in a file numbered 10 and then again in a file numbered 20, the
+override from 20 will take precedence).
+
+OPTIONS
+-------
+
+``-h``, ``--help``
+
+  Print help and exit.
+
+``--version``
+
+  Print program version and exit.
+
+``--targetdir <TARGET>``
+
+  Store ``gschemas.compiled`` in the ``TARGET`` directory instead of
+  ``DIRECTORY``.
+
+``--strict``
+
+  Abort on any errors in schemas. Without this option, faulty schema files are
+  simply omitted from the resulting compiled schema.
+
+``--dry-run``
+
+  Don’t write ``gschemas.compiled``. This option can be used to check
+  ``.gschema.xml`` sources for errors.
+
+``--allow-any-name``
+
+  Do not enforce restrictions on key names. Note that this option is purely
+  to facility the transition from GConf, and will be removed at some time
+  in the future.