3.0.0

• Get rid of constructor wrapper (#5)
• Cache instances are created using new keyword now, and full classes are exported instead of just a factory function.
• Now both Map-based and Object-based caches are symmetrically exported.

See benchmarks for how the two compare:

https://github.com/kibertoad/nodejs-benchmark-tournament/blob/master/cache-get-inmemory/_results/results.md
https://github.com/kibertoad/nodejs-benchmark-tournament/blob/master/cache-set-inmemory/_results/results.md