support spreadsheets.values.append method

[bpholt]

No description provided.

[codecov-io]

Codecov Report

Merging #168 (0bcdddc) into master (45e784d) will decrease coverage by 56.30%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           master     #168       +/-   ##
===========================================
- Coverage   95.77%   39.47%   -56.31%     
===========================================
  Files           5        5               
  Lines          71       76        +5     
===========================================
- Hits           68       30       -38     
- Misses          3       46       +43     

Impacted Files	Coverage Δ
...sheets4s/interpreters/RestSpreadsheetsValues.scala	0.00% <0.00%> (-100.00%)	⬇️
src/main/scala/gsheets4s/model.scala	90.90% <0.00%> (-5.97%)	⬇️
src/main/scala/gsheets4s/GSheets4s.scala	0.00% <0.00%> (-100.00%)	⬇️
...in/scala/gsheets4s/http/GSheets4sDefaultUrls.scala	0.00% <0.00%> (-100.00%)	⬇️
src/main/scala/gsheets4s/http/HttpClient.scala	0.00% <0.00%> (-93.11%)	⬇️

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[BenFradet]

Looks good, thanks a lot 👍
We might want to add an integration test leveraging appendAndGet though wdyt?