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ARROW-4196: [Rust] Add explicit SIMD vectorization for arithmetic ops in "array_ops"

Notes:

I moved the `divide` kernel but did not update it.  I will address this as part of [ARROW-4590](https://issues.apache.org/jira/browse/ARROW-4590?filter=-1) as I need to check for zero.  Up to this point I could ignore this and read/write to the padded region.

I tried to define a `ArrowSIMDType` trait but I felt it was worse than conditionally compiling the SIMD methods into `ArrowNumericType`.

Author: Paddy Horan <paddyhoran@hotmail.com>

Closes #3680 from paddyhoran/arithmetic-kernels and squashes the following commits:

d447bda <Paddy Horan> Fixed code comment lints
5e0bbd1 <Paddy Horan> Added benchmark for `arithmetic_kernels`
0f90968 <Paddy Horan> Added `arithmetic_kernels`
577d9c2 <Paddy Horan> Add SIMD associated type to `ArrowNumericType`