Move changelog to a folder and use single file entries

changelog/README.md

@@ -0,0 +1,34 @@
+How to add a new changelog entry to the pending changelog?
+==========================================================
+
+This will get copied to dlang.org and cleared when master gets
+merged into stable prior to a new release.
+
+```
+My fancy new feature X
+
+A long description of the new feature.
+-------
+import std.range;
+import std.algorithm.comparison;
+
+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!!!!"));
+-------
+```
+
+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:
+
+```
+../tools/changed.d -o ../dlang.org/changelog/pending.dd && make -C ../dlang.org -f posix.mak html
+```
+
+and then open `../dlang.org/web/changelog/pending.html` with your favorite browser.