Markdown format and release dates for the changelog

[jaykup26]

This modifies the CHANGELOG to:

• allow for issues, pull requests and commits to be automatically linked
• include the release dates
• make it a little more readable

This file could be renamed to CHANGELOG.md but another option to keep the filename the same is to simply add <!-- vim: syntax=Markdown --> at the top. This enables markdown while keeping the filename the same.

An example can be seen here:

https://github.com/jaykup26/bldc/blob/changelog/CHANGELOG

[vedderb]

Looks good! Qt 5.15 also supports markdown, so after a few updates they also look good in VESC Tool: