The Parse method now directly returns a report, rather than a list of
events that then need to be converted into a report. As part of this
change, the Event struct has also been moved to the gotest package. It's
now the responsibility of the parser to construct a gtr.Report.
When running `go test` without the `-v` flag, the output may not contain
everything that we expect. For example, no output is generated for
passing tests. Even for a failing test the output does not contain a
`=== RUN` line.
Currently, this resulted in us ignoring the test result since we
couldn't find an existing test to assign this result to. We should
however handle this situation gracefully, and just assume a test exists
when only encountering a test result line.
References #109
