message: Enable getting creditNotes by CreditNoteNumber
  Enable getting creditNotes by CreditNoteNumber much like you can get invoices by InvoiceNumber
diff: @@ -263,11 +263,14 @@ export class AccountingAPIClient extends BaseAPIClient {
  };
  public creditNotes = {
  - get: async (args?: { CreditNoteID?: string } & QueryArgs & PagingArgs & UnitDecimalPlacesArgs & HeaderArgs): Promise<CreditNotesResponse> => {
  + get: async (args?: { CreditNoteID?: string, CreditNoteNumber?: string } & QueryArgs & PagingArgs & UnitDecimalPlacesArgs & HeaderArgs): Promise<CreditNotesResponse> => {
  let endpoint = 'creditnotes';
  if (args && args.CreditNoteID) {
  endpoint = endpoint + '/' + args.CreditNoteID;
  delete args.CreditNoteID; // remove from query string
  + } else if (args && args.CreditNoteNumber) {
  + endpoint = endpoint + '/' + args.CreditNoteNumber;
  + delete args.CreditNoteNumber;
  }
  const header = this.generateHeader(args);
  endpoint += generateQueryString(args);
  