Arduino String/Stream add features

[PiotrekB416]

Add features to Arduino::String and Arduino::Stream
[x] String.insert
[x] Stream.readln or Stream.readLine

Requested by #152
More ideas are welcome

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (65633ce) 95.53% compared to head (b9ef2e8) 95.50%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #201      +/-   ##
==========================================
- Coverage   95.53%   95.50%   -0.03%     
==========================================
  Files          16       16              
  Lines        1075     1091      +16     
==========================================
+ Hits         1027     1042      +15     
- Misses         48       49       +1     

Files	Coverage Δ
api/Stream.h	100.00% <ø> (ø)
api/String.cpp	97.33% <100.00%> (+0.05%)	⬆️
api/String.h	90.90% <100.00%> (+0.90%)	⬆️
api/Stream.cpp	90.00% <83.33%> (-0.28%)	⬇️

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