Added ability to make a relay driver inverted

[andrewebdev]

I did not want to break any existing projects that already use the RelayDriver, but at the same time didn't want to create a completely new RelayDriver that has all the same functionality as the standard one, execpt that it's inverted.

For this reason I didn't updated the signature for NewRelayDriver and rather opted to add SetInverted which can then set this value after the initial instance was created.

[#648]

[codecov]

Codecov Report

Merging #674 into dev will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev     #674      +/-   ##
==========================================
+ Coverage   77.27%   77.29%   +0.01%     
==========================================
  Files         158      158              
  Lines       10935    10944       +9     
==========================================
+ Hits         8450     8459       +9     
  Misses       2030     2030              
  Partials      455      455

Impacted Files	Coverage Δ
drivers/gpio/relay_driver.go	92.15% <100%> (+1.68%)	⬆️

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[andrewebdev]

@deadprogram updated the PR; Inverted is now public

[deadprogram]

Thanks for working on this and making the requested changes, @andrewebdev now merging.