Prevent undefined elements

[mateonunez]

This PR fixes #29.

The solution is to add, before the return statement, a filter by Boolean, so undefined elements are filtered.

After doing several benchmarks between filter method, dynamic array, and the current solution, the result makes the filter method more performant.

Let me show you some data.

100K elements

Inserting 100K elements, search something, and limit by 1.

Current fixed allocation array

{ elapsed: '80μs', hits: [ undefined ], count: 0 } { timeSpent: '1072ms' }

Dynamic allocation array

{ elapsed: '82μs', hits: [], count: 0 } { timeSpent: '1117ms' }

Filtering results

{ elapsed: '75μs', hits: [], count: 0 } { timeSpent: '1080ms' }

1M elements

Inserting 1M elements, search something, and limit by 10.

{
  elapsed: '79μs',
  hits: [
    undefined, undefined,
    undefined, undefined,
    undefined, undefined,
    undefined, undefined,
    undefined, undefined
  ],
  count: 0
} { timeSpent: '11836ms' }

Dynamic allocation array

{ elapsed: '88μs', hits: [], count: 0 } { timeSpent: '11822ms' }

Filtering results

{ elapsed: '81μs', hits: [], count: 0 } { timeSpent: '11068ms' }

I also cleaned some variable names, (more readable in my opinion) by having them with the same name as the props returned in the function.

[micheleriva]

Awesome! Thank you for this!