refactor: use slack's internal markdown converter

[nobe4]

This is a companion PR that goes with
rneatherway/slack#4 to showcase what changes will look like in the gh-slack client.

It keeps the code as untouched as possible, and cleans the obsolete functions/types.

The code currently uses the latest commit on rneatherway/slack#4 and will need to be updated accordingly if/when that PR is merged.

Current version fetched with:

go get github.com/rneatherway/slack@d41e05cbe802da709eba14bffd8d6bf3716aa0d9

[rneatherway]

These changes look good to me 😄

Feel free to merge when ready.

[nobe4]

Thanks @rneatherway! It seems that by updating to a specific commit, I've polluted the go.mod file. Maybe we can create a release of slack? That might fix this?

Any thoughts?

[rneatherway]

Thanks @rneatherway! It seems that by updating to a specific commit, I've polluted the go.mod file. Maybe we can create a release of slack? That might fix this?

What do you mean when you say that you've polluted it? I don't have any trouble running the tests locally on this PR.

[nobe4]

I meant to say that the go.mod got a bunch of duplicate lines from installing the various commits by hands.

I don't really know if it's problematic but it looks unnecessary 🧐

[rneatherway]

Ah! I see what you mean now. Try running go mod tidy - that should clear it up 😄

[nobe4]

Indeed! Thanks 🙏