Starting to add resource metrics on runs of the tool.

[fosterbrereton]

We are looking to improve our understanding of how ORC utilizes the machine resources during processing, possibly in order to identify tradeoffs we can make in space v. time. This PR adds some initial memory footprint metrics to the end of the ORC run's output, along with a flag to enable it.

Here's an example output:

Resource metrics:
  String pool size / waste:
    0: 32 MiB (33554432) / 2.19 MiB (2292587) / 6.83%
    1: 32 MiB (33554432) / 2.21 MiB (2316317) / 6.90%
    2: 32 MiB (33554432) / 2.20 MiB (2310493) / 6.89%
    3: 32 MiB (33554432) / 2.31 MiB (2420043) / 7.21%
    4: 32 MiB (33554432) / 2.41 MiB (2527218) / 7.53%
    5: 32 MiB (33554432) / 2.13 MiB (2231512) / 6.65%
    6: 32 MiB (33554432) / 2.19 MiB (2292399) / 6.83%
    7: 32 MiB (33554432) / 2.16 MiB (2269894) / 6.76%
    8: 32 MiB (33554432) / 2.13 MiB (2237163) / 6.67%
    9: 32 MiB (33554432) / 2.26 MiB (2370840) / 7.07%
    10: 32 MiB (33554432) / 2.30 MiB (2411155) / 7.19%
    11: 32 MiB (33554432) / 2.32 MiB (2429004) / 7.24%
    12: 32 MiB (33554432) / 2.25 MiB (2355728) / 7.02%
    13: 32 MiB (33554432) / 2.42 MiB (2537523) / 7.56%
    14: 32 MiB (33554432) / 2.30 MiB (2408363) / 7.18%
    15: 32 MiB (33554432) / 2.30 MiB (2409418) / 7.18%
    16: 32 MiB (33554432) / 2.23 MiB (2337468) / 6.97%
    17: 32 MiB (33554432) / 2.43 MiB (2544395) / 7.58%
    18: 32 MiB (33554432) / 2.54 MiB (2664409) / 7.94%
    19: 32 MiB (33554432) / 2.15 MiB (2258360) / 6.73%
    20: 32 MiB (33554432) / 2.40 MiB (2514859) / 7.49%
    21: 32 MiB (33554432) / 2.35 MiB (2464329) / 7.34%
    22: 32 MiB (33554432) / 2.30 MiB (2411696) / 7.19%
    totals: 736 MiB (771751936) / 52.47 MiB (55015173) / 7.13%
  die footprint: 5.31 GiB (5702569584) 

[leethomason]

Looks good! Nice use of std::array as well.