PUBDEV-6338: In docs, add R example for slicing by date#3452

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ABartzGit wants to merge 2 commits intorel-yatesfrom PUBDEV-6338

+44-2

Commits on Mar 20, 2019

Initial checkin of 6338. Example currently fails.
Angela Bartz
committed

Commits on Apr 22, 2019

Adding R example for slice by date
Angela Bartz
committed