Add sqitch comparison

[halostatue]

Resolves #249 (for sqitch at least)

I recommend going through this commit by commit, as I changed some of the formatting in the README. I can undo those now that my notes have been added, but I think that they make the README easier to edit without making it harder to read (either raw or rendered).

I am impressed with what I see of dbmate, and think it’s better than the other tools that you have listed. I am not as convinced that it’s better than sqitch, but it is simpler than sqitch (there is a fairly large learning curve to sqitch in the same way as there’s a large learning curve to vim or git), which is worthwhile.

I think that it would be worthwhile for you to study sqitch and figure out what you can pinch to make dbmate better without compromising your simplicity. The first suggestion would be an optional verify step, which would be run after the deploy step and would invoke the revert step if it fails.

[Enrico204]

LGTM! For the change in the style of the links, I don't have a strong opinion (yet). Let's see what Adrian thinks about it :-)

Thanks, I didn't know sqitch before :-D