Live Json parsing

Changes

• You can now parse messages to json as they come in.
  You can also recover from errors while parsing and/or buffering while parsing.

  <script>
    import { source } from 'sveltekit-sse'
  
    const connection = source('/custom-event')
    const json = connection1.select('message').json(
      function onJsonParseError({error, currentRawValue, previousParsedValue}){
        console.error(`Could not parse "${currentRawValue}" as json.`, error)
        return previousParsedValue  // this will be the new value of the store
      }
    )
    $: console.log({$json})
  </svelte>

  When an parsing error occurs, onJsonParseError is invoked.
  Whatever this function returns will become the new value of the store, in the example above previousParsedValue, which is the previous (valid) value of the store.

Full Changelog: 0.5.3...0.6.0