add DeepSpeedZeroConfig __repr__ method

[stas00]

DeepSpeedZeroConfig object isn't being shown during startup

before:

[2020-12-10 21:24:11,820] [INFO] [config.py:648:print]   zero_config .................. 
<deepspeed.runtime.zero.config.DeepSpeedZeroConfig object at 0x7f32d4c0dbb0>

after this PR:

[2020-12-10 21:59:46,612] [INFO] [config.py:648:print]   zero_config .................. {
    "allgather_bucket_size": 500000000,
    "allgather_partitions": true,
    "contiguous_gradients": false,
    "cpu_offload": false,
    "elastic_checkpoint": true,
    "load_from_fp32_weights": true,
    "overlap_comm": false,
    "reduce_bucket_size": 500000000,
    "reduce_scatter": true,
    "stage": 0
}

Also I'm not sure about other files, but this file is in DOS format (\r\n/^M line ending)... is this by design?