Consider dropping `php-5.x` version supports

[peter279k]

As title, this issue should be considered.

Since the php-5.x versions are unsupported in PHP team, we should let this package require php-7.1+ versions at least.

The ext-mcrypt extension is deprecated since the php-7.1 is released.

I think we can do following works to resolve issue:

• Drop php-5.x versions.
• Drop ext-mcrypt support and let ext-sodium and ext-openssl extension supports.

Once this issue is accepted, I'm happy to work on this :).

[bitwombat]

Looks like phpaes might be abandonware! Can you fork it?