Add TypeScript typings

[yassernasc]

The this overhead at lines at: _read(this: this, size: number): void are a workaround to correct the 'this' value inside functions passed on constructor like:

const stream = new Readable({
  read(size) {
    t.is(this, stream) // in this case, 'this' was ReadableOptions 
  }
})

[kasperisager]

Looks like the only missing bit for the primary typings is the pipeline() function.

[yassernasc]

Added a more case at Readable.from because of this check: https://github.com/mafintosh/streamx/blob/7f745b9badded0f000247f06e8315387808aa9b1/index.js#L786

[yassernasc]

beautiful