Feat: Allow use of remote storage

[jsutlovic]

I was attempting to use exiffield with S3 storage, but the storage backend doesn't support the path operation since the files are not local. I've implemented a workaround that allows exiffield to be used regardless of whether the files are remote.

[coveralls]

Pull Request Test Coverage Report for Build 292887961

• 7 of 7 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.5%) to 95.556%

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Totals
Change from base Build 292883824:	-0.5%
Covered Lines:	172
Relevant Lines:	175

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💛 - Coveralls

[escaped]

Thanks for this great contribution. Will have a proper look at your changes soon, but at a first glance, they look good :)

[escaped]

LGTM! Thanks for your contribution :)