Issue 81: Added getFirstItem method

[maryiabydanova]

resolves #81

• Add getFirst function into IImporter interface (not in IImporterLegacy)
• Implement getFist in a Importer class (not in ImporterLegacy)
• Update sample in Readme (use getFist) - docs: added usage sample for getFirstItem method siemienik.github.io#16
• Update/Add at least one test which check it.

Question:
not quite sure what readme sample is referenced in the todo. Where would be the best place to add a usage sample?

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[Siemienik]

@maryiabydanova Thank you for your contribution 🥇

not quite sure what readme sample is referenced in the todo. Where would be the best place to add a usage sample?

Actually, recently I moved documentation from repo to the website https://siemienik.com/ .
For these changes, I suggest https://github.com/Siemienik/siemienik.github.io/blob/master/docs/xlsx-import-readme.md .

[codecov]

Codecov Report

Merging #198 (a5b7688) into master (f2502d6) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #198   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           55        55           
  Lines         1078      1087    +9     
  Branches       154       154           
=========================================
+ Hits          1078      1087    +9     

Flag	Coverage Δ
xlsx-import	100.00% <100.00%> (ø)
xlsx-renderer	100.00% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
packages/xlsx-import/src/Importer.ts	100.00% <100.00%> (ø)
...sx-import/tests/integration/vertical-lists.test.ts	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f2502d6...a5b7688. Read the comment docs.

[Siemienik]

Thank you, @maryiabydanova! You did it perfectly 🥇