Adding MacAddress, MacAddress8

[mrengineer7777]

Adding New Classes MacAddress, MacAddress8 in the style of IPAddress. Note I didn't include Printable, as I don't understand how that works (edit: see updates below). If someone else wants to add it later, they are welcome to do so. This is my first time contributing to this repository, so please feel free to point out any mistakes.

This library originated on arduino-esp32 (espressif/arduino-esp32#6667). It was suggested that I contribute to the Arduino core as well :)

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[codecov-commenter]

Codecov Report

Merging #162 (a740b1c) into master (e03b653) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #162   +/-   ##
=======================================
  Coverage   96.00%   96.00%           
=======================================
  Files          13       13           
  Lines         827      827           
=======================================
  Hits          794      794           
  Misses         33       33           

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[mrengineer7777]

Final version, ready for review. See test project here: https://github.com/mrengineer7777/MA_Test

[mrengineer7777]

It seems there is no interest so I will be deleting this PR soon.

[aentinger]

Sorry, this fell through the cracks. In any case adding test code would be much appreciated.

@facchinm what do you think re integrating this to the core API?