add PSR-16 support

[renanbr]

No description provided.

[renanbr]

Tests are green in PHP 5.6 and 7, but failing in those version:

• 5.5, because cache/simple-cache-bridge requires 5.6;
• HHVM, I have no idea what happens

I can go further if you consider this patch pertinent

[Kevinrob]

Nice! Thank you for the PR @renanbr !

HHVM isn't supported anymore by Doctrine\Cache... I think that I will remove it (see doctrine/cache#219)
For PHP 5.5... Is it still used? 🤔

[Kevinrob]

@renanbr When you write I can go further if you consider this patch pertinent. What did you mean? Is there anything that you want to add before I merge the PR?

[renanbr]

I was talking about PHP 5.5 test failure, but I think I solved it changing cache/simple-cache-bridge constraint requirement from ^1.0 to ^0.1 || ^1.0, because 0.1.0 works on PHP 5.5.

From my side it's ready to merge :-)