move to esp32 standard logging style

[webmonkey]

replaced Serial.print*() style logging with log_*() style logging

resolves #129

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• Describe the scope of your change--i.e. what the change does and what parts
  of the code were modified. This will help us understand any risks of integrating
  the code.

All references to Serial.print(), Serial.printf() and Serial.println() have been replaced with log_e(), log_w() etc style ESP32 logging.

• Describe any known limitations with your change. For example if the change
  doesn't apply to a supported platform of the library please mention it.

I did not change the default progress callback which prints dots to the Serial Console

• Please run any tests or examples that can exercise your modified code. We
  strive to not break users of the code and running tests/examples helps with this
  process.

I have tested the library against my project that uses the library. I have not tested it against all of the examples in this repo.

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