YAML output fix

[omaralvarez]

As is, when using a YAML parser there is a Scanner error: mapping values are not allowed in this context.

This PR fixes #5.

The problematic chunk of the output is for example:

Performance Results For Rank 0:
  Timer: total
    CallCount:  1
    AvgPerCall:   6.0009
    Total:        6.0009
    PercentLoop:   101.79
  Timer: loop
    CallCount:  1
    AvgPerCall:   6.0009
    Total:        6.0009
    PercentLoop:   101.79

It should instead output:

Performance Results For Rank 0:
  - Timer: total
    CallCount:  1
    AvgPerCall:   6.0009
    Total:        6.0009
    PercentLoop:   101.79
  - Timer: loop
    CallCount:  1
    AvgPerCall:   6.0009
    Total:        6.0009
    PercentLoop:   101.79

With these changes the YAML output is compliant with the standard version 1.2.