Adding namespaces for the Mailchecker class on the PHP Platform

[taimursalman]

The following points pertain to MailChecker being used in PHP code.

As the library is being loaded via composer, the files get auto-loaded, and using require to load them again will be an unnecessary step. This PR aims to use namespaces instead. Some advantages of using namespaces over require statements are

1. Namespace Isolation: Namespaces provide a way to isolate your code from the user's code, reducing the chance of naming conflicts.
2. Improved Readability: When users import classes or functions via namespaces, their code becomes more readable because they can see exactly where a particular class or function is coming from.
3. Easy Updates: If you need to release a new version of your library with improvements or bug fixes, users can simply update their Composer dependencies, and the latest version of your library will be automatically used.

[dmouse]

can you include the autoload definition in the composer.json file, this can replace the classmap.

thank you for your contribution!

"autoload": {
    "psr-4": {
      "Fgribreau\\": "platform/php"
    }
  },

Update:

This is a breakthrough in the library, if you include the namespace this is not compatible with the previous class definition

[FGRibreau]

This is a breakthrough in the library, if you include the namespace this is not compatible with the previous class definition

Exactly, I will have to release a new major version of mailchecker but indeed it makes sense.

@taimursalman like @dmouse said, could you please update your PR to include the autoload definition in the composer.json file?

[taimursalman]

Certainly! Will do

Edit: The commit has been added

[FGRibreau]

@dmouse what do you think of the PR? Good to go?

[dmouse]

@FGRibreau after this I think is a good idea include some documentation about how to upgrade to the previous version to this new version with namespace.

Edit:
I send this other PR just to update the doc #419