Add optional duration and executionTime parameters

[afbjorklund]

When reporting results from a previously recorded test run,
rather than streaming the results from a test being run now.

Closes #21

[afbjorklund]

One could consider having both of these two, in the same feature:

ls --full-time test.json

go-test-report -e "date goes here" <test.json

Like --input test.json, would use the modification date of that file.

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The duration would still have to be reported separately, though.

It is not being recorded, in the JSON output from go test -json

[afbjorklund]

Replaced with:

• Add optional parameters for running with gotestsum #62