feat: add support for multiple images per url, close #41

[codecov[bot]]

Codecov Report

Merging #62 (2f49b58) into master (b99724d) will increase coverage by 0.08%. The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master      #62      +/-   ##
============================================
+ Coverage     97.54%   97.62%   +0.08%     
- Complexity      203      210       +7     
============================================
  Files             6        6              
  Lines           529      548      +19     
============================================
+ Hits            516      535      +19     
  Misses           13       13              

Files	Coverage Δ
src/Extensions/GoogleImageExtension.php	100.00% <100.00%> (ø)
src/SitemapGenerator.php	96.21% <100.00%> (ø)