CMakeParseArguments: replace by native cmake_parse_arguments command

Implement a native `cmake_parse_arguments` command that is fully
compatible with the documented behaviour of the previous implementation.
Leave the CMakeParseArguments module empty but existing for
compatibility.

Help/command/cmake_parse_arguments.rst

@@ -0,0 +1,78 @@
+cmake_parse_arguments
+---------------------
+
+``cmake_parse_arguments`` is intended to be used in macros or functions for
+parsing the arguments given to that macro or function.  It processes the
+arguments and defines a set of variables which hold the values of the
+respective options.
+
+::
+
+  cmake_parse_arguments(<prefix> <options> <one_value_keywords>
+                        <multi_value_keywords> args...)
+
+
+The ``<options>`` argument contains all options for the respective macro,
+i.e.  keywords which can be used when calling the macro without any value
+following, like e.g.  the ``OPTIONAL`` keyword of the :command:`install`
+command.
+
+The ``<one_value_keywords>`` argument contains all keywords for this macro
+which are followed by one value, like e.g. ``DESTINATION`` keyword of the
+:command:`install` command.
+
+The ``<multi_value_keywords>`` argument contains all keywords for this
+macro which can be followed by more than one value, like e.g. the
+``TARGETS`` or ``FILES`` keywords of the :command:`install` command.
+
+When done, ``cmake_parse_arguments`` will have defined for each of the
+keywords listed in ``<options>``, ``<one_value_keywords>`` and
+``<multi_value_keywords>`` a variable composed of the given ``<prefix>``
+followed by ``"_"`` and the name of the respective keyword.  These
+variables will then hold the respective value from the argument list.
+For the ``<options>`` keywords this will be ``TRUE`` or ``FALSE``.
+
+All remaining arguments are collected in a variable
+``<prefix>_UNPARSED_ARGUMENTS``, this can be checked afterwards to see
+whether your macro was called with unrecognized parameters.
+
+As an example here a ``my_install()`` macro, which takes similar arguments
+as the real :command:`install` command:
+
+.. code-block:: cmake
+
+   function(MY_INSTALL)
+       set(options OPTIONAL FAST)
+       set(oneValueArgs DESTINATION RENAME)
+       set(multiValueArgs TARGETS CONFIGURATIONS)
+       cmake_parse_arguments(MY_INSTALL "${options}" "${oneValueArgs}"
+                             "${multiValueArgs}" ${ARGN} )
+
+       # ...
+
+Assume ``my_install()`` has been called like this:
+
+.. code-block:: cmake
+
+   my_install(TARGETS foo bar DESTINATION bin OPTIONAL blub)
+
+After the ``cmake_parse_arguments`` call the macro will have set the
+following variables::
+
+   MY_INSTALL_OPTIONAL = TRUE
+   MY_INSTALL_FAST = FALSE (was not used in call to my_install)
+   MY_INSTALL_DESTINATION = "bin"
+   MY_INSTALL_RENAME = "" (was not used)
+   MY_INSTALL_TARGETS = "foo;bar"
+   MY_INSTALL_CONFIGURATIONS = "" (was not used)
+   MY_INSTALL_UNPARSED_ARGUMENTS = "blub" (nothing expected after "OPTIONAL")
+
+You can then continue and process these variables.
+
+Keywords terminate lists of values, e.g.  if directly after a
+one_value_keyword another recognized keyword follows, this is
+interpreted as the beginning of the new option.  E.g.
+``my_install(TARGETS foo DESTINATION OPTIONAL)`` would result in
+``MY_INSTALL_DESTINATION`` set to ``"OPTIONAL"``, but as ``OPTIONAL``
+is a keyword itself ``MY_INSTALL_DESTINATION`` will be empty and
+``MY_INSTALL_OPTIONAL`` will therefore be set to ``TRUE``.