CI runs against all major PHP versions from 5.3 to 7.3

[martin-georgiev]

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[martin-georgiev]

This PR will ignore PHP 7.2 failures as the project is not yet migrated to be fully compatible with that version. @Miljar I can do the necessary work in a separate PR once current is merged.

[Miljar]

@martin-georgiev I have started working on a reworked version some time ago, but haven't been able to complete it. All work for the Exiftool implementation still needs to be ported. I really should dedicate some more time to it to get a 1.0 version out the door :/

[martin-georgiev]

@Miljar Thank you for the speedy collaboration.
I will look later this week for some low hanging fruits like making the project compatible with 7.2 and eventually will add more steps to the CI pipeline.

[Miljar]

@martin-georgiev Thanks for your PR! Any help is greatly appreciated. Also, you brought this back to my attention, so I'll try to give php-exif some much needed love ;)