Add insecure option, include bucket name in AWS credentials, best-eff…

…ort+zoom flag (#18)

* implement minZ maxZ logic

* add tiles_c

* revert image.go changes

* actually loop sources backwards and reimplement opaque check

* actually loop sources backwards and reimplement opaque check

* insecure https

* add insecure option

* include bucketname in AWS credentials env variables

* fix zoom level mismatch skip in combination with bestEffort flag

Co-authored-by: Alexander Waldenmaier <[email protected]>

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