Fix and simplify building docs and schemas (#441)

Fix and simplify building docs and schemas

1. Do an in-source build of derived schemas instead of building into build and checking that the files match.
2. Fix paths of installed docs, which were failing on me
3. Consolidate docs into same cmakelists that generates schema files
4. Trang is usually available as an executable, so find it with find_program.
5. Add doc dependencies to package.xml

Signed-off-by: Dan Rose <dan@digilabs.io>

cmake/Modules/FindTrang.cmake

@@ -0,0 +1,53 @@
+# Copyright(c) 2020 ADLINK Technology Limited and others
+#
+# This program and the accompanying materials are made available under the
+# terms of the Eclipse Public License v. 2.0 which is available at
+# http://www.eclipse.org/legal/epl-2.0, or the Eclipse Distribution License
+# v. 1.0 which is available at
+# http://www.eclipse.org/org/documents/edl-v10.php.
+#
+# SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
+#
+
+#[=======================================================================[.rst:
+FindTrang
+---------
+Finds Trang, an xml schema transpiler
+
+Result Variables
+^^^^^^^^^^^^^^^^
+
+This will define the following variables:
+
+``Trang_FOUND``
+  True if the system has the Foo library.
+``Trang_VERSION``
+  The version of the Foo library which was found.
+``Trang_TRANG_CMD``
+  List of command line args to run Trang.
+``Trang_TRANG_EXECUTABLE``
+  Path to the Trang executable file
+
+#]=======================================================================]
+
+find_program(Trang_TRANG_EXECUTABLE trang)
+
+execute_process(
+  COMMAND "${Trang_TRANG_EXECUTABLE}"
+  ERROR_VARIABLE trang_output
+)
+if(trang_output MATCHES "Trang version ([0-9]+)")
+  set(TRANG_VERSION "${CMAKE_MATCH_1}")
+else()
+  message(ERROR "Could not parse version from Trang output: '${trang_output}'")
+  set(TRANG_VERSION "0")
+endif()
+
+set(Trang_TRANG_CMD "${Trang_TRANG_EXECUTABLE}")
+
+include(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(
+  Trang
+  REQUIRED_VARS Trang_TRANG_CMD
+  VERSION_VAR TRANG_VERSION
+)