doc: update credits and changelog, reference the base-gtkmm project.

doc/changelog.dox

@@ -100,6 +100,9 @@ See also:
 -   Added @ref Platform::GlfwApplication::KeyEvent::Key::World1 and
     @ref Platform::GlfwApplication::KeyEvent::Key::World2
 -   Added @ref Platform::EmscriptenApplication::KeyEvent::Key::Semicolon
+-   New [base-gtkmm](https://github.com/mosra/magnum-bootstrap/tree/base-gtkmm)
+    bootstrap project for using Magnum together with gtkmm (see
+    [mosra/magnum-bootstrap#24](https://github.com/mosra/magnum-bootstrap/pull/24))
 
 @subsubsection changelog-latest-new-vk Vk library
 
@@ -265,7 +268,9 @@ See also:
 
 @subsection changelog-latest-documentation Documentation
 
--   Various fixes (see [mosra/magnum#390](https://github.com/mosra/magnum/pull/390))
+-   Various fixes and clarifications (see
+    [mosra/magnum#390](https://github.com/mosra/magnum/pull/390),
+    [mosra/magnum#418](https://github.com/mosra/magnum/pull/418))
 
 @section changelog-2019-10 2019.10
 

doc/credits.dox

@@ -131,6 +131,9 @@ Are the below lists missing your name or something's wrong?
     improvements
 -   **Ivan Sanz Carasa** ([\@isc30](https://github.com/isc30)) --- buildsystem
     improvements
+-   **Jackson Campolattaro** ([\@JacksonCampolattaro](https://github.com/JacksonCampolattaro))
+    --- documentation improvements, [base-gtkmm](https://github.com/mosra/magnum-bootstrap/tree/base-gtkmm)
+    bootstrap project
 -   **Jan Dupal** ([\@JanDupal](https://github.com/JanDupal)) --- Homebrew
     package for `magnum-bindings`
 -   **Jonathan Hale** ([\@Squareys](https://github.com/Squareys)) ---

doc/platform.dox

@@ -172,9 +172,10 @@ following code listing.
 @note Fully contained application using with manual Magnum initialization on
     top of Qt toolkit is available in `base-qt` branch of
     [Magnum Bootstrap](https://github.com/mosra/magnum-bootstrap/tree/base-qt)
-    repository. A similar project, but for wxWidgets is in the
+    repository. Similar project, but for wxWidgets and gtkmm are in the
     [base-wxwidgets](https://github.com/mosra/magnum-bootstrap/tree/base-wxwidgets)
-    branch.
+    and [base-gtkmm](https://github.com/mosra/magnum-bootstrap/tree/base-gtkmm)
+    branches.
 @note
     There's also an example showing @ref examples-triangle-plain-glfw "usage of plain GLFW to render a basic triangle".