doc: attempt to get rid of doxygenlayouts and doxyfiles.

Generate doc root doxygenlayout file, as well as devices stuff, based on main
Makefile $(TARGETS) and template files. Avoids painfull sync/merge of 20 files+
when adding a new device.
bonus : allow to build only one device doc easily (make TARGETS=stm32f0 doc)

regression: we currently loose device "fancy" naming as device name is
guessed (toUpper()..) from folder name.

scripts/gendoxylayout.py

@@ -0,0 +1,68 @@
+#!/usr/bin/env python
+# This python program generates parameters for the linker script generator feature.
+
+# This file is part of the libopencm3 project.
+#
+# 2019 Guillaume Revaillot <g.revaillot@gmail.com>
+#
+# This library is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this library. If not, see <http://www.gnu.org/licenses/>.
+
+from xml.etree import ElementTree
+
+import argparse
+
+
+parser = argparse.ArgumentParser(prog='gendoxylayout')
+parser.add_argument("--template", required=True)
+parser.add_argument("--out", required=True)
+parser.add_argument("--target")
+parser.add_argument("devices", nargs='*')
+args = parser.parse_args()
+
+class CommentedTreeBuilder(ElementTree.TreeBuilder):
+    def __init__(self, *args, **kwargs):
+        super(CommentedTreeBuilder, self).__init__(*args, **kwargs)
+
+    def comment(self, data):
+        self.start(ElementTree.Comment, {})
+        self.data(data)
+        self.end(ElementTree.Comment)
+
+tree = ElementTree.parse(args.template, ElementTree.XMLParser(target=CommentedTreeBuilder()))
+parent_map = {c:p for p in tree.iter() for c in p}
+for element in tree.iter(tag=ElementTree.Comment):
+	if ("#devices#" in element.text):
+		idx = (list(parent_map[element]).index(element))
+		for device in args.devices:
+			tab = ElementTree.Element('tab')
+
+			tab.set("visible", "yes")
+			tab.set("title", str(device).upper())
+			tab.set("intro", "")
+
+			if (args.target != None):
+				if (device == args.target):
+					tab.set("type", "modules")
+				else:
+					tab.set("type", "user")
+					tab.set("url", "../../" + device + "/html/modules.html")
+			else:
+				tab.set("type", "user")
+				tab.set("url", "../" + device + "/html/modules.html")
+
+			parent_map[element].insert(idx, tab)
+			idx = idx+1;
+		parent_map[element].remove(element)
+
+tree.write(args.out)