Add custom snapshot serializers (#1741)

[anilanar]

Summary
Add custom snapshot serializers as a configurable option, add it to "Configuration" docs.

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[codecov-io]

Current coverage is 87.47% (diff: 100%)

Merging #1842 into master will not change coverage

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  Files            38         38          
  Lines          1222       1222          
  Methods           0          0          
  Messages          0          0          
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  Hits           1069       1069          
  Misses          153        153          
  Partials          0          0          

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[cpojer]

Sorry for getting back to this so late.

This is a really solid PR. I'll merge it tomorrow!

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