Add gather macro#213

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TonyLianLong wants to merge 11 commits intoqueryverse:masterfrom

TonyLianLong:add-gather-and-spread

Commits on Nov 6, 2018

Add gather macro
TonyLianLong
committed

Commits on Nov 18, 2018

Update @gather macro to match the new format
TonyLianLong
committed

Commits on Nov 21, 2018

Parse `-:Name` syntax
TonyLianLong
committed

Commits on Nov 30, 2018

Add tests for gather operator
TonyLianLong
committed

Commits on Jan 20, 2019