Help: Improve wording of CMAKE_CURRENT_FUNCTION_LIST_DIR docs

The original wording was somewhat confusing in talking about rendering of
templates. While technically correct, a less experienced user may not know
that terminology. The wording has been updated to more clearly describe the
example usage.

The old way of implementing the example is not "bad", it was the only way to do
things before the CMAKE_CURRENT_FUNCTION_LIST_DIR variable was added.
The example has been updated to remove the Bad/Good captions to reflect this.
Indentation of the examples was also fixed to make them conform to the guidelines.

Help/variable/CMAKE_CURRENT_FUNCTION_LIST_DIR.rst

@@ -4,30 +4,38 @@ CMAKE_CURRENT_FUNCTION_LIST_DIR
 When executing code inside a :command:`function`, this variable
 contains the full directory of the listfile that defined the current function.
 
-It is quite common practice in CMake that modules use some additional files
+It is quite common practice in CMake for modules to use some additional files,
-(e.g., templates to render).  And the code typically did the following:
+such as templates to be copied in after substituting CMake variables.
+In such cases, a function needs to know where to locate those files in a way
+that doesn't depend on where the function is called.  Without
+``CMAKE_CURRENT_FUNCTION_LIST_DIR``, the code to do that would typically use
+the following pattern:
 
 .. code-block:: cmake
-    :caption: Bad
 
-    set(_THIS_MODULE_BASE_DIR "${CMAKE_CURRENT_LIST_DIR}")
+  set(_THIS_MODULE_BASE_DIR "${CMAKE_CURRENT_LIST_DIR}")
 
-    function(foo)
+  function(foo)
-      configure_file(
+    configure_file(
-        "${_THIS_MODULE_BASE_DIR}/some.template.in"
+      "${_THIS_MODULE_BASE_DIR}/some.template.in"
-        some.output
+      some.output
-      )
+    )
-    endfunction()
+  endfunction()
 
-Using this variable inside a function eliminates the neccessity of the
+Using ``CMAKE_CURRENT_FUNCTION_LIST_DIR`` inside the function instead
-additional one with "global" scope:
+eliminates the need for the extra variable which would otherwise be visible
+outside the function's scope.
+The above example can be written in the more concise and more robust form:
 
 .. code-block:: cmake
-    :caption: Good
 
-    function(foo)
+  function(foo)
-      configure_file(
+    configure_file(
-        "${CMAKE_CURRENT_FUNCTION_LIST_DIR}/some.template.in"
+      "${CMAKE_CURRENT_FUNCTION_LIST_DIR}/some.template.in"
-        some.output
+      some.output
-      )
+    )
-    endfunction()
+  endfunction()
+
+See also :variable:`CMAKE_CURRENT_FUNCTION`,
+:variable:`CMAKE_CURRENT_FUNCTION_LIST_FILE` and
+:variable:`CMAKE_CURRENT_FUNCTION_LIST_LINE`.