ftf 0.4.0

Run functional tests from a variety of formats
Documentation
tests:
    - name: "Compile ftf"
      binary: "cargo"
      args:
        - "build"

    - name: "Valid echo"
      binary: "./target/debug/ftf"
      args:
        - "-f"
        - "./tests/fixtures/yaml/echo.yaml"

    - name: "Invalid echo"
      binary: "./target/debug/ftf"
      args:
        - "-f"
        - "./tests/fixtures/yaml/invalid_echo.yaml"
      exit_code: 1

    - name: "Long tests"
      binary: "sleep"
      args:
        - "3"
      exit_code: 0

    - name: "stdout is contains() and not eq()"
      binary: "echo"
      args:
        - "some long string"
      stdout: "long"