HttpClientException should be exported.

[abal1000x]

Is your feature request related to a problem?

Yes. When i got HttpClientException from teledart, i couldn't catch it, because the exception class are not exported.

Describe the solution you'd like

Refactor the HttpClientException out from src/util/http_client.dart and export it to the teledart.dart

Some code snippet would help?

  Teledart teledart = Teledart(...);

  // This will throws HttpClientException with code 429, because its <10 minutes opened.
  teledart.close();

Additional context

None.

[HeySreelal]

Since #262 is merged, this issue also can be closed now. HttpClientException is also being exported now.

cc: @DinoLeung