Document PHP version requirement

[juho-jaakkola]

Currently there is no information of the required PHP version.

Make sure to add it at least to the require section in composer.json, for example:

{
    "require" : {
        "php" : "^5.5"
    }
}

This way composer automatically checks the version when the library is being installed to a project.

[icc]

The original target version was 5.2.5 or higher. I guess we should keep that as long as we support Drupal 6.

[juho-jaakkola]

PHP 5.2? Ouch, support for it ended already in 2011. This further reaffirms my thought that the project would benefit from using Semver-compatible branches for different versions. I added #12 for further discussion.

[Tuurlijk]

On February 24th 2016, Drupal 6 will reach end of life and no longer be supported.

https://www.drupal.org/forum/general/news-and-announcements/2015-11-09/drupal-6-end-of-life-announcement

Can we please move on here? The library needs some refactoring and polish.

[djoudi]

i think is realy to upgrade to php 7.*

[otacke]

@djoudi I think @fnoks tried to explain why 5.3 is still set as a minimum requirement at #64 (comment) just three weeks ago.