Add quote_style option to csv IO functions

[jdbarillas]

Implements the QuoteStyle options for CsvWriter into to_csv and dump_csv (with :necessary as default)

New behavior:

iex(2)> df = Explorer.Datasets.fossil_fuels() |> Explorer.DataFrame.head(2)
iex(3)> dump_csv(df)                                                       
{:ok,
 "year,country,total,solid_fuel,liquid_fuel,gas_fuel,cement,gas_flaring,per_capita,bunker_fuels\n2010,AFGHANISTAN,2308,627,1601,74,5,0,0.08,9\n2010,ALBANIA,1254,117,953,7,177,0,0.43,7\n"}
iex(4)> dump_csv(df, [quote_style: :always])                               
{:ok,
 "\"year\",\"country\",\"total\",\"solid_fuel\",\"liquid_fuel\",\"gas_fuel\",\"cement\",\"gas_flaring\",\"per_capita\",\"bunker_fuels\"\n\"2010\",\"AFGHANISTAN\",\"2308\",\"627\",\"1601\",\"74\",\"5\",\"0\",\"0.08\",\"9\"\n\"2010\",\"ALBANIA\",\"1254\",\"117\",\"953\",\"7\",\"177\",\"0\",\"0.43\",\"7\"\n"}

iex(5)> dump_csv(df, [quote_style: :non_numeric])                          
{:ok,
 "\"year\",\"country\",\"total\",\"solid_fuel\",\"liquid_fuel\",\"gas_fuel\",\"cement\",\"gas_flaring\",\"per_capita\",\"bunker_fuels\"\n2010,\"AFGHANISTAN\",2308,627,1601,74,5,0,0.08,9\n2010,\"ALBANIA\",1254,117,953,7,177,0,0.43,7\n"}

TO DO:

• Tests

This is my first experience with Rust so any feedback would be appreciated.

[billylanchantin]

Thanks, this seems useful!

Rust code looks good at a glance. And yes we'll need a test or two (on the Elixir side).

[jdbarillas]

Tests added

[josevalim]

We need documentation on the supported values for this function and we are good to go :)

[jdbarillas]

Done, let me know if there's any additional places needed

[philss]

@jdbarillas thank you! :D