amazonka-s3: Rewrite requests to use vhost bucket endpoints

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Closes #630
Closes #628
Closes #610

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This is my first PR doing serious wrangling to requests, so I'd appreciate a close review.

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I tested creating/destroying buckets in us-east-1 and eu-west-1, as well as GetBucketLocation and putting/getting small objects.

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It appears that S3 now has a dotted regional endpoint for each region, so I removed this. I made test requests to s3.us-east-1.amazonaws.com.

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Skipping because boto skips it too:

https://github.com/boto/botocore/blob/04d1fae43b657952e49b21d16daa86378ddb4253/botocore/utils.py#L1131-L1135

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@AriFordsham @RobertFischer Be great if you had a chance to test this PR too.

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Ping @K0Te - this may also fix your issue.

[AriFordsham]

@endgame Thank you! I'm glad this vital package isn't bit-rotting.

I would love to test, but I would need to pull out some old code - I'll see what I can do.

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@AriFordsham In case it helps: https://github.com/gilt/kms-s3/pull/4 is an example PR where I modernised some amazonka usage. You'll need to change the revs in the cabal.project file, or do the stack equivalent.

The changelog also provides an overview of how library conventions have changed:

amazonka/amazonka/CHANGELOG.md

Lines 10 to 21 in ca9540e

	- Enums (sum types) have been replaced with pattern synonyms. (Thanks @rossabaker)
	- This reduces GHC memory usage on some large packages (notably `amazonka-ec2`), as well as makes them more robust against new enum values in regions, responses, etc.
	- Naming
	- Record smart constructors (previously `describeInstances`, `getObject`, etc.) are now strictly prefixed with `new`, such as `newDescribeInstances`.
	- Generated lenses are no longer exported from the top-level `Network.AWS.<name>` module - instead a `Network.AWS.<name>.Lens` module is provided.
	- Generated lenses no longer use mnemonic or heuristically assigned prefixes such as `dirsrsInstances` and instead strictly prefix using the type name `describeInstances_instances` - following the form `<type>_<field>`.
	- You may prefer to use a library like [`generic-lens`](https://hackage.haskell.org/package/generic-lens) instead of the long lens names.
	- Exports
	- Every `amazonka-*` package re-exports the `Network.AWS.Prelude` module.
	- All type constructors (Such as record constructors) are now exported by default.

[brendanhay]

LGTM! I'd rather avoid extra dependencies if possible, at least until everything has been pared back (looking at you, conduit) - but regex-posix is pretty lightweight so lets' ship it and worry about that later.

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I'd rather avoid extra dependencies if possible

Me too, but I chose to take on a regex package so the code would have a more obvious correspondence with the boto equivalent.

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@AriFordsham @RobertFischer @K0Te I'm merging this now but it would be good if you tested it.