Update changelog for 1.0 release

[Conengmo]

@ocefpaf let's do a 1.0 release! If you agree, here's what I think we should do:

I will:

• Add a changelog for Branca.
• Merge this PR.

Afterwards, you can:

• Make a Branca 0.7.0 release.
• Make a Folium 1.0.0 release.

What are your thoughts on this?

[martinfleis]

Shall we include #1793 and possibly python-visualization/branca#134 before releasing?

[Conengmo]

• FIX #1787 Bump Jquery Version #1793 requires more work to get it through, I don't think that PRs going to cut it.
• fix calculation of color index branca#134 seems good on surface, but we have to take a good look to verify what's being changed.

Both of which I haven't spent time on yet.

I'm okay with waiting for these two for a 1.0 release. But maybe we can do a 0.15.0 then in the meantime, since somebody asked for that: #1730 (comment)

[ocefpaf]

It is a long weekend here but I'll try to get to this ASAP. If not, next Monday.

[martinfleis]

I guess that we should resolve #1803 before releasing as well.

[Conengmo]

I'll use these when we make a 0.15.0, but this PR can be closed.