Add Changelog for 1.7.0

[straight-shoota]

Preview: https://github.com/crystal-lang/crystal/blob/feature/changelog-1.7/CHANGELOG.md

[Blacksmoke16]

Somewhat related, I think we're nearing the point where we should trim down the changelog file. At least drop pre 1.0.0 stuff.

Terraform goes a bit further where they only have entries for current minor version on each version branch: https://github.com/hashicorp/terraform/blob/main/CHANGELOG.md

At the moment this is what I get when trying to look at the changelog, which isn't a great experience :/

EDIT: It seems to render fine when I open it in an incognito window...not sure what causes the discrepancy there.

[beta-ziliani]

Maybe a matter of cache? In any case, I think it's not a bad idea to just keep the last major ones in CHANGELOG.md and make a CHANGELOG.0.md (or the like) for the < 1.0.0 one.