adding support for the "data-src" attribute to img

[jaywhj]

Fixed issue #65

1. Added use of data-src where src is used. data-src is a custom attribute that complies with the HTML5 specification for data sources
2. Prioritize data-src over src, because data-src is usually the "real resource path", while src may be a placeholder or null value, e.g., when loading images lazily, src tends to be a placeholder, and data-src is the real image

[Wcowin]

Excellent work, my friend.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (c94b061) to head (036d066).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #66   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          116       117    +1     
=========================================
+ Hits           116       117    +1     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.