Add request(), hasNextPage(), and requestNextPage() (#887)

* Add support for all rippled APIs, including subscriptions.
* Add support for arbitrary stream message types.
* Note that rippled APIs take amounts in drops.
* request() will be available in ripple-lib version 1.0.0+

src/ledger/accountinfo.ts

@@ -35,7 +35,7 @@ export default async function getAccountInfo(
   // 1. Validate
   validate.getAccountInfo({address, options})
   // 2. Make Request
-  const response = await this._request('account_info', {
+  const response = await this.request('account_info', {
     account: address,
     ledger_index: options.ledgerVersion || 'validated'
   })