examples for QGIS 3.1

[slmanali]

these examples doesn't work with Qgis 3.10.
any notice to make them work?

[ThomasG77]

See my PRs on the project https://github.com/qgis/QGIS-Code-Examples/pulls/ThomasG77

[aman2000jaiswal14]

Added example recently https://github.com/aman2000jaiswal14/QGIS-CPP-API-QT5