fix: consolidate the API of AsyncParser and parseAsync

[juanjoDiaz]

Closes #468

[coveralls]

Coverage remained the same at 100.0% when pulling 16db2e4 on juanjoDiaz:consolidate_async_parsers into 55aa0c7 on zemirco:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 3a67571 on juanjoDiaz:consolidate_async_parsers into 471f5a7 on zemirco:master.

[juanjoDiaz]

I'm also considering if it make sense the current API:

• fromInput allows you to set the input which can be a stream, an array or a single object.
• throughTransform allows you to add transforms to the input stream.
• toOutput allows you to set the output stream.
• promise returns a promise that resolves when the stream ends or errors. Takes a boolean parameter to indicate if the resulting CSV should be kept in-memory and be resolved by the promise.

or if they should be replaced by something simpler and more aligned with the sync API like

• parse(input) which takes an input (stream, array or object) and returns the CSV.

The methods throughTransform and toOutput are just wrappers around pipe and don't really provide anything.

The method promise is very similar to the finished method that has been added to the stream/promise API in node.
The only difference is that it can gather the whole JSON in a string and resolve that.

I can see 2 options here:
I could move the promise method to either the JSON2CSVTransform so you can do

const csv = await asyncParse.parse(data).promise();

I could add a utils module with a StreamToString class that gathers the string and exposes a promise method that resolves when the stream ends, so the user can do

const streamToString =  new StreamToString();
asyncParse.parse(data).pipe(streamToString);
const csv = await asyncParse.parse(data).pipe(streamToString).promise()

I like the second one better.
This PR already includes the ArrayAsStream method wich is basically ArrayToStream.
So having StreamToString seems pretty consistent.

Thoughts?

[knownasilya]

I like option 2 as well

[juanjoDiaz]

This should be good to merge.

[knownasilya]

Can we link to the docs for nodes stream module?

[knownasilya]

Where does myData come from in this example, and why does it have default?

[juanjoDiaz]

myData is the same myData as in all the other examples.. any array.
It doesn't have default. I'll remove that.

[juanjoDiaz]

All feedback has been fixed I think.