Many open source projects already provide a Changelog / News / Release-Notes file. There's not a standard format for them, but common formatting practices.

Freshcode autoupdating understands plain text, MarkDown and ReStructuredText variants following the common scheme:

 1.0.0 (2014-08-20)
 ------------------
   * Added foo and bar.
   * Fixed file saving bugs.

 0.9.9 (2013-12-31)
 ------------------
   * Adds better manpages.
   * Removes old logos.

Most importantly releases should be ordered newest first.

• Each version header must contain a version number.
• And an ISO date or timestring.
• Changes, fixes should be in some form of bullet list.

Quite a few custom formats are still supported. In particular release headlines are often marked up using MarkDown or Wiki headlines instead:

## 1.2.0 / 2014-07-17

   * Changes xyz, baz.

The version number may be prefixed by Changes for or Version or just a v prefix. The date is commonly enclosed in parens, but may be separated using slashes, hyphens, etc.

Bullet point lists can obviously use other list markers than *. A more recent development is using the markup for semantics:

===== 1.3.0 - 2015-01-01 =====
   - Removed something.
   * Changes feature.
   + Added function.

It's also common and therefore supports to provide MarkDown subheadings between change lists:

#### Version 1.7.5 (2015-02-30)

## Core:

  * Changes xyz.
  * Fixes bar.

## UI:

  * New logo.

Here it's advisable to add colons for subheadings. Just like change entries should always be complete sentences including trailing dot.

Freshcodes autoupdate supports one extension to the common formats, in that it permits release tags in version headlines:

 ## v2.0.0-rc1 minor bugfix prerelease (2015-05-20)

This avoids lengthy version suffix chains. But again, is non-standard.

State: functional, testing