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ARROW-3898: [Example] parquet-arrow example has compilation errors

When compiling example, reader-writer.cc, it shows following compilation errors:

no member named 'cout' in namespace 'std'

  PARQUET_THROW_NOT_OK(arrow::PrettyPrint(*array, 4, &std::cout));

in multiple places.

Fix:
Add the #include<iostream>
Test:
make passed

Author: Wes McKinney <wesm+git@apache.org>
Author: wangmiao1981 <wm624@hotmail.com>

Closes #3049 from wangmiao1981/example and squashes the following commits:

ecca664a2 <Wes McKinney> Build all examples in examples/parquet when PARQUET_BUILD_EXAMPLES=ON
64d51b214 <wangmiao1981> add include file