arrow

ARROW-5189: [Rust] [Parquet] Format / display individual fields within a parquet row

Hi,

I'm working on a simple cli app to sample and analyze parquet files.
And couldn't find simple way to get a simple string representation of each column within a `Row`.

All `Field`s in a row already implement `fmt::Display` but there is now way to format individual fields.
Since the `Row#fields`  is not exposed by the api. Which i assume is by design.

Having a way to format individual fields seems like a common problem,
so I came up with a `RowFormatter` which provides a way to access the field as a `fmt::Display`.

```rust
use parquet::record::RowFormatter;

// ...

let row = make_row(vec![
    ("id".to_string(), Field::Int(5)),
    ("name".to_string(), Field::Str("abc".to_string()))
]);

println!("row id   : {}", row.fmt(0).unwrap());
println!("row name : {}", row.fmt(1).unwrap());
```

I'm just getting started with Rust so please let me know if i can do anything better here..

Author: Fabio B. Silva <fabio.bat.silva@gmail.com>

Closes #4174 from FabioBatSilva/row-fmt and squashes the following commits:

2cae53af <Fabio B. Silva> fmt fixes
ef94b5de <Fabio B. Silva> Simplify RowFormatter#fmt by removing Result
ceb91194 <Fabio B. Silva> Add RowFormatter to pub api
df522752 <Fabio B. Silva>  format / display fields within a Row