Modifications on HashMap and HashSet

[tur11ng]

• Changed the inner representation of entries in HashMap
• Added the Keys() and Values() methods to both HashMap and HashSet data structures
• Did benchmarks on the results and compared my fork with yours. This repository was used with custom modifications. Found that they did not differ in time and I think my implementation extends the interface making it a bit more useful.

Thanks you for your time.

[zyedidia]

What's the reason for changing the inner representation of entries? I think the addition of the Keys and Values methods is fine, but I'm not sure the other changes are necessary.