Move changelog to a folder and use single file entries

changelog/README.md

@@ -0,0 +1,42 @@
+This directory will get copied to dlang.org and cleared when master gets
+merged into stable prior to a new release.
+
+How to add a new changelog entry to the pending changelog?
+==========================================================
+
+Create a new file in the `changelog` folder. It should end with `.dd` and look
+similar to a git commit message. The first line represents the title of the change.
+After an empty line follows the long description:
+
+```
+My fancy title of the new feature
+
+A long description of the new feature in `std.range`.
+It can be followed by an example:
+-------
+import std.range : padLeft, padRight;
+import std.algorithm.comparison : equal;
+
+assert([1, 2, 3, 4, 5].padLeft(0, 7).equal([0, 0, 1, 2, 3, 4, 5]));
+
+assert("Hello World!".padRight('!', 15).equal("Hello World!!!!"));
+-------
+and links to the documentation, e.g. $(REF drop, std, range) or
+$(REF_ALTTEXT a custom name for the function, drop, std, range).
+
+Links to the spec can look like this $(LINK2 $(ROOT_DIR)spec/module.html, this)
+and of course you can link to other $(LINK2 https://forum.dlang.org/, external resources).
+```
+
+The title can't contain links (it's already one).
+For more infos, see the [Ddoc spec](https://dlang.org/spec/ddoc.html).
+
+Preview changes
+---------------
+
+If you have cloned the [tools](https://github.com/dlang/tools) and [dlang.org](https://github.com/dlang/dlang.org) repo),
+you can preview the changelog with:
+
+```
+make -C ../dlang.org -f posix.mak pending_changelog
+```