source_group: Add options create groups matching directory tree

Add `TREE` and `PREFIX` arguments to enable this behavior.

Help/command/source_group.rst

@@ -2,15 +2,27 @@ source_group
 ------------
 
 Define a grouping for source files in IDE project generation.
+There are two different signatures to create source groups.
 
-.. code-block:: cmake
+::
 
   source_group(<name> [FILES <src>...] [REGULAR_EXPRESSION <regex>])
+  source_group(TREE <root> [PREFIX <prefix>] [FILES <src>...])
 
 Defines a group into which sources will be placed in project files.
 This is intended to set up file tabs in Visual Studio.
 The options are:
 
+``TREE``
+ CMake will automatically detect, from ``<src>`` files paths, source groups
+ it needs to create, to keep structure of source groups analogically to the
+ actual files and directories structure in the project. Paths of ``<src>``
+ files will be cut to be relative to ``<root>``.
+
+``PREFIX``
+ Source group and files located directly in ``<root>`` path, will be placed
+ in ``<prefix>`` source groups.
+
 ``FILES``
  Any source file specified explicitly will be placed in group
  ``<name>``.  Relative paths are interpreted with respect to the
@@ -25,11 +37,13 @@ explicitly lists the file with ``FILES`` will be favored, if any.
 If no group explicitly lists the file, the *last* group whose
 regular expression matches the file will be favored.
 
-The ``<name>`` of the group may contain backslashes to specify subgroups:
+The ``<name>`` of the group and ``<prefix>`` argument may contain backslashes
+to specify subgroups:
 
 .. code-block:: cmake
 
   source_group(outer\\inner ...)
+  source_group(TREE <root> PREFIX sources\\inc ...)
 
 For backwards compatibility, the short-hand signature