Investigate/improve support of multi-part files and compression

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Overview

It includes:

• clarification of resource.hash/bytes for multipart files
• support of compressed multipart files for goodtables
• check-sums validation for goodtables

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Added various tests to the libs.

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The summary is that FD stack (hence goodtables-py):

• supports multi-part resource
• supports compressed resources
• DOESN'T support multi-part compressed resources (https://github.com/frictionlessdata/tabulator-py/issues/267)