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ARROW-4038: [Rust] Implement boolean AND, OR, NOT array ops

- Implements boolean AND, OR, NOT operations in `array_ops`
- Removes all uses of `unwrap()` in array_ops and replaces with `?`
- Improve error messages

Author: Andy Grove <andygrove73@gmail.com>

Closes #3189 from andygrove/ARROW-4038 and squashes the following commits:

69518d7 <Andy Grove> add tests
a38d9a9 <Andy Grove> add docs for all array_ops and add explicit handling for case where both sides are null
661e2af <Andy Grove> improve error message
36b9171 <Andy Grove> Implement boolean AND, OR, NOT operations, remove unwraps and improve error message