docs: Add release notes, replacing the upgrading notes

This patch replaces the upgrading notes, which focused only on
backwards-incompatible changes, with more detailed release notes.

docs/relnotes.md

@@ -0,0 +1,93 @@
+
+# Release notes
+
+This file contains notes for each release, summarizing changes and explicitly
+noting backward-incompatible changes or known security issues.
+
+
+## 1.1 (2019-10-26)
+
+- Added hooks for aliases resolution.
+- Added rspamd integration in the default post-data hook.
+- Added chasquid-util aliases-add subcommand.
+- Expanded SPF support.
+- Documentation and test improvements.
+- Minor bug fixes.
+
+
+## 1.0 (2019-07-15)
+
+No backwards-incompatible changes. No more are expected within this major
+version.
+
+- Fixed a bug on early connection deadline handling.
+- Make DSN tidier, especially in handling multi-line errors.
+- Miscellaneous test improvements.
+
+
+## 0.07 (2019-01-19)
+
+No backwards-incompatible changes.
+
+- Send enhanced status codes.
+- Internationalized Delivery Status Notifications (DSN).
+- Miscellaneous test improvements.
+- DKIM integration examples and test.
+
+
+## 0.06 (2018-07-22)
+
+No backwards-incompatible changes.
+
+- New MTA-STS (Strict Transport Security) checking.
+
+
+## 0.05 (2018-06-05)
+
+No backwards-incompatible changes.
+
+- Lots of new tests.
+- Added a how-to and manual pages.
+- Periodic reload of domaininfo, support removing entries manually.
+- Dovecot auth support no longer considered experimental.
+
+
+## 0.04 (2018-02-10)
+
+No backwards-incompatible changes.
+
+- Add Dovecot authentication support (experimental).
+- Miscellaneous bug fixes to mda-lmtp and tests.
+
+
+## 0.03 (2017-07-15)
+
+**Backwards-incompatible changes:**
+
+- The default MTA binary has changed. It's now maildrop by default.
+  If you relied on procmail being the default, add the following to
+  `/etc/chasquid/chasquid.conf`: `mail_delivery_agent_bin: "procmail"`.
+- chasquid now listens on a third port, submission-on-TLS.
+  If using systemd, copy the `etc/systemd/system/chasquid-submission_tls.socket`
+  file to `/etc/systemd/system/`, and start it.
+
+
+Release notes:
+
+- Support submission (directly) over TLS (submissions/smtps/port 465).
+- Change the default MDA binary to `maildrop`.
+- Add a very basic MDA that uses LMTP to do the mail delivery.
+
+
+## 0.02 (2017-03-03)
+
+No backwards-incompatible changes.
+
+- Improved configuration checks and safeguards.
+- Fall back through the MX list on errors.
+- Experimental MTA-STS implementation (disabled by default).
+
+
+## 0.01 (2016-11-03)
+
+Initial release.