Allow custom PSR 6 cache

[DivineOmega]

This PR allows developers to make use of any PSR 6 compliance cache.

It also improves the existing caching, to prevent unnecessary re-caching.

[coveralls]

Pull Request Test Coverage Report for Build 137

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 89.362%

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Totals
Change from base Build 124:	0.0%
Covered Lines:	42
Relevant Lines:	47

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💛 - Coveralls

[DivineOmega]

Closing, as this will be replaced by #22.