Fix ordering of debounced events

[dfaust]

I wasn't able to reproduce the panic, but the new sort logic should fix the issue and it's also stable now.

We should release this fix as soon as possible.

Fixes #636.

[maratik123]

Seem with that total algorithmic complexity has O(n^2). May be it is need to use binary heap or something like this to track min_time?

[dfaust]

Using BinaryHeap improves performance a bit. Especially in scenarios with many files.

I didn't commit the benchmark because I don't know if it's useful enough. But here are the results. Unfortunately they are a bit over the place, so I'm not sure how reliable they are:

sort-events/sort_events with 10 files and 100k events each
    new:   [328.05 ms 330.98 ms 334.31 ms]
    old:   [408.45 ms 453.59 ms 512.18 ms] +37.042%

sort-events/sort_events with 1k files and 1k events each
    new:   [398.06 ms 401.66 ms 405.87 ms]
    old:   [448.35 ms 454.64 ms 462.24 ms] +13.190%

sort-events/sort_events with 100k files and 10 events each
    new:   [841.49 ms 906.83 ms 1.0303 s]
    old:   aborted after 10 minutes