Allow `resources` to be specified as a string

[Lnk2past]

When specifying a resource to copy to the test folder, one must specify the src and dst, even if the name is going to be preserved. A resource should be allowed to be specified as a string, and contest should figure out the src and dst from that. i.e. allow:

# see https://github.com/Lnk2past/contest
executable: ./bin/main.exe
test-cases:
    - name: test-01
      resources:
        - data