Allow psr/simple-cache 3.x

[colinodell]

Description

Adds support for using this library with psr/simple-cache 2.x and 3.x without breaking backward-compatibility.

Closes #119

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes.

• Unit tests
• Spec Tests
• Integration tests / Manual Tests

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[colinodell]

Some notes to assist with your review :)

[sighphyre]

@colinodell This looks great! Thanks for doing this!

I'm happy with this but I'd like @RikudouSage to take a glance and give the nod

[RikudouSage]

This looks great! There's just one small thing and then I'm more than happy to merge!