Automatic merge of T1.5.1-799-gb02a6e5d3 and 14 pull requests

- Pull request #570 at 3539862: Experimental glTF 2.0 support with PBR lighting
- Pull request #839 at d00beb9: First phase of https://blueprints.launchpad.net/or/+spec/additional-cruise-control-parameters
- Pull request #876 at f92de76: docs: add source for documents previously on website to source Documentation folder
- Pull request #882 at a055bca: Blueprint/train car operations UI window
- Pull request #885 at 8f94333: feat: Add notifications to Menu
- Pull request #886 at 6c0785b: Scene viewer extension to TrackViewer
- Pull request #892 at 1f5ba4c: Signal Function OPP_SIG_ID_TRAINPATH
- Pull request #896 at 5866028: First implementation of https://blueprints.launchpad.net/or/+spec/specific-sounds-for-ai-trains
- Pull request #897 at 0a9d939: feat: Improved system information collection
- Pull request #899 at f5a3bd8: Duplex steam engines - Booster Engine addition
- Pull request #903 at 6c9da3f: Downloading route content (Github, zip)
- Pull request #907 at 9b0b04f: Bug fix for https://bugs.launchpad.net/or/+bug/2047300 Dynamic tracks disappear after long tunnel
- Pull request #908 at 4b4afe3: feat: supports switching adhesion precisions
- Pull request #911 at 6834af0: docs: Add refactoring as a special type of PR

Author: openrails-bot

Docs/Contributing.md

@@ -18,7 +18,7 @@ If you've got a feature suggestion for Open Rails, please report it in [our road
 
 You are free to make any modifications to the Open Rails code that you like; that's how open source works. However, if you'd like your feature to be included in the official version, there is a process to ensure that the community agrees and to review the code for potential issues prior to inclusion.
 
-In most cases, you can get started immediately with making the changes and creating a pull request. We do ask for some additional steps to be taken for some bugs and all new features, but they can come before or after the pull request. Please feel free to share ideas and proposals as pull requests!
+In most cases, you can get started immediately with making the changes and creating a pull request. We have _additional requirements_ for some bugs and all new features, but they can come before or after the pull request is created. Please feel free to share ideas and proposals as pull requests!
 
 **Note:** You must fork the Open Rails repository before you start working on it. We do not allow you to push branches to the official repository.
 
@@ -28,19 +28,25 @@ In most cases, you can get started immediately with making the changes and creat
 
 If you'd like to improve the [documentation](./), [manual](../Source/Documentation/Manual), or [translations](../Source/Locales) you can get started immediately.
 
-There are no requirements for the pull request.
+There are no additional requirements for the pull request.
 
 ### Contributed projects
 
 If you'd like to improve the [contributed projects](../Source/Contrib) you can get started immediately.
 
-There are no requirements for the pull request.
+There are no additional requirements for the pull request.
+
+### Refactoring process
+
+If you'd like to refactor the existing code you can get started immediately, but please have a look at our [architecture requirements](#architecture-requirements). We welcome architectural discussions on our [forum](http://www.elvastower.com/forums/index.php?/forum/256-developing-features/).
+
+There are no additional requirements for the pull request.
 
 ### Bug process
 
 If you'd like to fix a bug, you can get started immediately. If the fix turns out to be very small, you do not even need a bug report. Otherwise, you will need to make sure it has been reported on [our bug tracker on Launchpad](https://bugs.launchpad.net/or). If it has not, you can report the bug *and* fix it!
 
-There are no requirements for creating the pull request.
+There are no additional requirements for _creating_ the pull request.
 
 These things must be done in the required order: