Fix changelog format

[rpeshkov]

Seems like current changelog format is taken from https://keepachangelog.com, however one main rule is not followed: version headers should lead to comparison between versions. That's why in current changelog versions are shown in square brackets, while they should be links.

Example of full changelog here: https://github.com/olivierlacan/keep-a-changelog/blob/master/CHANGELOG.md

Link in changelog for version 1.0: olivierlacan/keep-a-changelog@v0.3.0...v1.0.0

[rpeshkov]

I've tracked down commits that was made right before marketplace updates and which version was that

8caf817 -> 0.1.1
55d7bb9 -> 0.1.2
107d7b0 -> 0.1.3
770811b -> 0.5.0

So, this way we can put tags on each of those commits and update changelog accordingly so it'll be easier to track down what actually changed between versions.