Add support to postgres range fields

[berinhard]

Fixes #70
Fixes #81

This PR add supports to Postgres's range fields.

[berinhard]

@anapaulagomes and @amureki I think we can relase a new version of model bakery once we merge this. Although, the ideal release would also have #81 fixed and merged in.

[anapaulagomes]

Sounds good to me. But @berinhard did you mean #81 or another issue?

[berinhard]

Yep, because while working on this PR to fix the issue #70, I noticed that there were other range types besides DecimalRangeField. In this PR I focused only on fixing the numeric ranges but the issue #81 covers the others.

In my opinion, a more consistent release would cover all range fields, so that's why I think it would be nice for us to have #81 fixed as well =)

[anapaulagomes]

Thanks for adding these fields to Model Bakery, @berinhard! 🏅 I've got only minor comments and one question about letting DecimalRangeField separated from the other fields added.

[berinhard]

@anapaulagomes I've updated this PR and also fixed the conflict in the Changelog. Can you review it again, please?

[anapaulagomes]

LGTM! 🏆

[berinhard]

@anapaulagomes sorry but by the time you've left your approval, I was adding support to DateRangeField and DateTimeRangeField (4 minutes difference =S). The code is pretty much the same as before, but introducing 2 new generators. I'll wait for you review on the 2 new commits to merge this PR and release a new version as well.

[berinhard]

@amureki can you review this PR? @anapaulagomes will be offline for a while, so it's up to the 2 of us to keep on with the project =)

[amureki]

Hey Bernardo!
Great work, this is definitely needed change. :)

I had some small comments to be checked, feel free to drop me a line about those!