Return iterator of arrow record batches to JS

[kylebarron]

Motivation: Parquet and Arrow are chunked formats. Therefore we shouldn't need to wait for the entire dataset to load/parse before getting some data back.

However I'm still not aware of a way to return an iterable or an async iterable from rust to js. To get around this, I think we can "drive" the iteration from JS. Essentially this:

import * as wasm from 'parquet-wasm';

const arr = new Uint8Array(); // Parquet bytes
// name readSchema to align with pyarrow api?
const parquetFile = new wasm.ParquetFile(arr);
const schemaIPC = parquetFile.schema();
for (let i = 0; i < parquetFile.numRowGroups; i++) {
  const recordBatchIPC = parquetFile.readRowGroup(i);
}

And ideally we'll have an async version of this too

[kylebarron]

This is also closed with #296

[kylebarron]

This is also closed with #296