Filter type by condition specified in callback function

[Havelis]

I was trying to filter out items by type guard and I notice that filter is implemented just in the way that the returned SubDocumentArray has not any information about doc's fields. So I add implementation for filter which returned type is based on the condition specified in callback function.

But, I'm not sure about the S[] & SubDocumentArrayNoId<S> in return type. It is right or it should return just S[]?

Thanks for any advice.

[codecov-io]

Codecov Report

Merging #39 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master     #39   +/-   ##
======================================
  Coverage    90.9%   90.9%           
======================================
  Files           5       5           
  Lines          33      33           
  Branches        5       5           
======================================
  Hits           30      30           
  Misses          3       3

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[faltysad]

+1 on this

[rongyadong]

+1 on this as well