doc: further iterate on plugin CMake usage, update changelog.

doc/changelog.dox

@@ -53,6 +53,11 @@ See also:
     MSVC 2017. See also [mosra/magnum-bootstrap#18](https://github.com/mosra/magnum-bootstrap/issues/18),
     [mosra/magnum#343](https://github.com/mosra/magnum/pull/343) and
     [mosra/magnum#354](https://github.com/mosra/magnum/issues/354).
+-   When using Magnum as a CMake subproject, it now puts all binaries into a
+    common directory to simplify `PATH` handling and dynamic plugin loading.
+    For more information see @ref cmake-subproject,
+    [mosra/magnum#357](https://github.com/mosra/magnum/issues/357) and
+    [mosra/magnum-plugins#63](https://github.com/mosra/magnum-plugins/issues/63).
 -   New @ref Image::pixels(), @ref ImageView::pixels() and
     @ref Trade::ImageData::pixels() accessors for convenient direct access to
     pixel data of any image

doc/cmake.dox

@@ -70,10 +70,16 @@ repositories into your project (as a Git submodule, bundling a downloaded
 archive etc.) and use @cb{.cmake} add_subdirectory() @ce. With that approach
 you don't need to care about `FindCorrade.cmake` / `FindMagnum.cmake`, however
 the usual tradeoffs when bundling code apply --- slower full rebuilds, IDEs
-having more to parse etc.
+having more to parse etc. In this case, the
+@ref building-features "build-time options" are @cmake set() @ce before
+the @cmake add_subdirectory() @ce call. Note that, unless you require CMake
+3.13 at least, it's needed to use the `CACHE ... FORCE` arguments
+[in order to have the options set properly](https://cmake.org/cmake/help/latest/policy/CMP0077.html). For example:
 
 @code{.cmake}
 add_subdirectory(corrade EXCLUDE_FROM_ALL) # so only things you use are built
+
+set(WITH_ANYIMAGEIMPORTER ON CACHE BOOL "" FORCE) # enable what you need
 add_subdirectory(magnum EXCLUDE_FROM_ALL)
 
 find_package(Magnum REQUIRED ...) # see below
@@ -106,7 +112,24 @@ add_subdirectory(corrade EXCLUDE_FROM_ALL)
 add_subdirectory(magnum EXCLUDE_FROM_ALL)
 @endcode
 
-@section cmake-find-module Finding the package and its component
+Please note that in case of the (by default) dynamic plugins, because these are
+loaded at runtime, CMake doesn't know we need them to be built --- one option
+is to list them explicitly like shown below, another (but uglier) is to not use
+`EXCLUDE_FROM_ALL` on the `magnum` subdirectory, so everything is always built
+implicitly.
+
+@code{.cmake}
+set(WITH_ANYIMAGEIMPORTER ON CACHE BOOL "" FORCE)
+set(WITH_ANYSCENEIMPORTER ON CACHE BOOL "" FORCE)
+add_subdirectory(magnum EXCLUDE_FROM_ALL)
+
+# So the AnyImageImporter / AnySceneImporter gets built implicitly
+add_custom_target(plugins ALL DEPENDS
+    Magnum::AnyImageImporter
+    Magnum::AnySceneImporter)
+@endcode
+
+@section cmake-find-module Finding the package and its components
 
 Basic usage is:
 

doc/plugins.dox

@@ -42,16 +42,16 @@ embedded systems that don't support dynamic loading, built statically into the
 executable. Depending on the target platform requirements, different set of
 plugins can be deployed for different platforms.
 
-The @ref building "Magnum repository" contains a few basic plugins for opening
+The @ref building "core Magnum repository" contains a few basic plugins for
-simple formats, such as TGA images or WAV audio files. These plugins are
+opening simple formats, such as TGA images or WAV audio files. These plugins
-included because the file formats are so simple that no external library is
+are included because the file formats are so simple that no 3rd party libraries
-needed for loading their contents and thus they are suitable for quick demos
+are needed  for loading their contents and thus they are suitable for quick
-and prototyping without needing to deal with additional dependencies.
+demos and prototyping without needing to deal with additional dependencies.
 
-Additional plugins (such as importers for PNG and JPEG images, TrueType fonts
+Additional plugins (such as importers for PNG and JPEG images, glTF scenes,
-etc.) are available in the @ref building-plugins "Magnum Plugins" repository.
+TrueType fonts etc.) are available in the @ref building-plugins "Magnum Plugins"
-Majority of these plugins depends on external libraries, thus not all of them
+repository. Majority of these plugins depends on external libraries, thus not
-might be available on all platforms.
+all of them might be available on all platforms.
 
 @section plugins-types Plugin interfaces
 
@@ -91,7 +91,7 @@ whole lifetime of all plugin instances created using it.
 
 @section plugins-dependencies Plugin dependencies
 
-Some plugins have dependencies, for example the @ref Trade::OpenGexImporter "OpenGexImporter"
+Some plugins have dependencies, for example the @ref Trade::TinyGltfImporter "TinyGltfImporter"
 plugin uses @ref Trade::AnyImageImporter "AnyImageImporter" to load texture
 data. The dependency loading is done automatically, but in some cases it's
 across plugin types (for example the @ref Text::MagnumFont "MagnumFont" plugin