chore(docs): make changelogs visible on docsrs

Split changelog file to make it more comprehensible when reading and
also make it a part of documentation so it'll be more discoverable
by the users. This change also makes it possible for rust code inside
the changelogs to be tested with `cargo`.

Co-authored-by: Kirill Chibisov <contact@kchibisov.com>

src/changelog/mod.rs

@@ -0,0 +1,75 @@
+//! # Changelog and migrations
+//!
+//! All notable changes to this project will be documented in this module,
+//! along with migration instructions for larger changes.
+//!
+// Put the current entry at the top of this page, for discoverability.
+// See `.cargo/config.toml` for details about `unreleased_changelogs`.
+#![cfg_attr(unreleased_changelogs, doc = include_str!("unreleased.md"))]
+#![cfg_attr(not(unreleased_changelogs), doc = include_str!("v0.29.md"))]
+
+#[doc = include_str!("v0.29.md")]
+pub mod v0_29 {}
+
+#[doc = include_str!("v0.28.md")]
+pub mod v0_28 {}
+
+#[doc = include_str!("v0.27.md")]
+pub mod v0_27 {}
+
+#[doc = include_str!("v0.26.md")]
+pub mod v0_26 {}
+
+#[doc = include_str!("v0.25.md")]
+pub mod v0_25 {}
+
+#[doc = include_str!("v0.24.md")]
+pub mod v0_24 {}
+
+#[doc = include_str!("v0.23.md")]
+pub mod v0_23 {}
+
+#[doc = include_str!("v0.22.md")]
+pub mod v0_22 {}
+
+#[doc = include_str!("v0.21.md")]
+pub mod v0_21 {}
+
+#[doc = include_str!("v0.20.md")]
+pub mod v0_20 {}
+
+#[doc = include_str!("v0.19.md")]
+pub mod v0_19 {}
+
+#[doc = include_str!("v0.18.md")]
+pub mod v0_18 {}
+
+#[doc = include_str!("v0.17.md")]
+pub mod v0_17 {}
+
+#[doc = include_str!("v0.16.md")]
+pub mod v0_16 {}
+
+#[doc = include_str!("v0.15.md")]
+pub mod v0_15 {}
+
+#[doc = include_str!("v0.14.md")]
+pub mod v0_14 {}
+
+#[doc = include_str!("v0.13.md")]
+pub mod v0_13 {}
+
+#[doc = include_str!("v0.12.md")]
+pub mod v0_12 {}
+
+#[doc = include_str!("v0.11.md")]
+pub mod v0_11 {}
+
+#[doc = include_str!("v0.10.md")]
+pub mod v0_10 {}
+
+#[doc = include_str!("v0.9.md")]
+pub mod v0_9 {}
+
+#[doc = include_str!("v0.8.md")]
+pub mod v0_8 {}