Default formatter

[floringogianu]

rlog really needs a nice default formatter instead of doing:

log_fmt = (
        "[{0:6d}/{ep_cnt:5d}] R/ep={R_ep:8.2f}, V/step={V_step:8.2f}"
        + " | steps/ep={steps_ep:8.2f}, fps={fps:8.2f}."
)

log.info(log_fmt, **summary)

every single time.

A bit tricky because there can be many registered rlog.Metric and the output can get quite large. Maybe provide an abridged with one log per ~80 characters line and a full version, with maybe one metric on a line?

• Abridged:

01:21:42 [I] a2c.valid@825000: R/ep= 48.11, RunR/ep=  4.47 | steps/ep=  939.99, fps=  626.12.

• Full:

 training  ...........................  6983772 steps | 1 day, 6:47:40 elapsed.
    | ep_cnt ........................................................ 2951.000.
    | rw_per_ep ...................................................... -18.000.
    | rw_per_step ..................................................... -0.007.
    | max_q ............................................................ 2.167.
    | loss ............................................................. 0.064.
    | aux_loss ......................................................... 0.020.
    | training_fps .................................................. 2918.315.
    | sampling_fps .................................................... 91.197.