Added support for multiline JSON parsing

[DeiNile]

It is pretty common to send JSON over websockets, and it can be rather limiting to be forced to "minify" the JSON string, especially for local testing. The new '-j --json' flag is supposed to alleviate that. The primary way this is alleviated is by allowing for multiline inputs. Secondarily, by leveraging the built in JSON.parse() method we can check to see if the inputs produce a valid JSON string, and determine that the multiline input is terminated. Finally, as inspired by the Scala REPL, two consecutive empty lines resets the input.

Here are some samples of what this looks like while it is running:

$ wscat -j -c ws://websocket-echo.com
Connected (press CTRL+C to quit)
> {}
< {}
> []
< []
> {
|   "foo": "bar",
|   "hello": "world"
| }
< {
  "foo": "bar",
  "hello": "world"
}
> 42
< 42
> "hello world"
< "hello world"
> [
|   1,
|   2
|   ,3]
< [
  1,
  2
  ,3]