Re-export Arrow and Parquet crates from DataFusion

[returnString]

Which issue does this PR close?

Closes #36.

What changes are included in this PR?

• The datafusion crate now re-exports its versions of arrow and parquet
• The benchmarks and datafusion-examples crates have been updated to make use of these exports in lieu of declaring their own dependencies on the arrow-rs repo

Bonus subsection: not changed

• The various Ballista crates have not been updated to make use of this at present as I'm not familiar enough with Ballista's needs and current status
• datafusion-examples still manually depends on the arrow-rs repo for Flight support, as DataFusion doesn't use this currently

Are there any user-facing changes?

This only provides users with an extra option for referencing arrow and parquet, without breaking existing setups - we should probably add this to an installation/usage section of the user guide once that settles a bit though.

[codecov-commenter]

Codecov Report

Merging #39 (de2a6ef) into master (713ba10) will not change coverage.
The diff coverage is 0.00%.

❗ Current head de2a6ef differs from pull request most recent head 1ddbbf4. Consider uploading reports for the commit 1ddbbf4 to get more accurate results

@@           Coverage Diff           @@
##           master      #39   +/-   ##
=======================================
  Coverage   75.83%   75.83%           
=======================================
  Files         135      135           
  Lines       23152    23152           
=======================================
  Hits        17557    17557           
  Misses       5595     5595           

Impacted Files	Coverage Δ
benchmarks/src/bin/nyctaxi.rs	0.00% <ø> (ø)
benchmarks/src/bin/tpch.rs	38.86% <0.00%> (ø)
datafusion-examples/examples/flight_server.rs	0.00% <0.00%> (ø)
datafusion-examples/examples/simple_udaf.rs	0.00% <ø> (ø)

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[jorgecarleitao]

LGTM. Thanks a lot, @returnString !

Could you rebase / address conflicts?

[alamb]

I agree -- super helpful @returnString . Thank you

[returnString]

No problem at all :) Just rebased to fix up the conflicts with the benchmark refactoring.

[andygrove]

I merged this into master locally and the tests pass so I will merge this. Thanks @returnString !