Drop support for PHP 5 and set new minimum to 7.2

[Korvin Szanto]

Our current minimum PHP version is 5.4, this has the following effects:

• Automated testing in CI slow and requires 7 separate environments to test all versions
• We contribute to an ecosystem of packages based on versions of PHP that are unsupported and potentially insecure
• We limit ourselves to old language functionality and can't make use of better patterns like type hinting

I propose we up the minimum PHP requirement for 0.18.0 to PHP 7.2 and update all implementations and interfaces to make use of scalar type hinting and return types.

Related Work:

• 6e5e107 Update to PHP 7.2 minimum with working tests
• Update documentation to reflect this update

[Korvin Szanto]

Let's do this for 1.0.0 instead of 0.18.0. We'd like to leave 0.x as backwards compatible as possible.

[Korvin Szanto]

#476 is the beginnings of this

[Anatoly Nekhay]

How is it going? Is this project still supported?

[Tobias Nyholm]

This is fixed in master.