Extend options to decrease requests

[wimurk]

Currently the API has a rate limit of 1000 per API or IP. This is acceptable when it comes to the API Key limit, but the IP rate limit is killing my App.

Currently i have 24 users using the API. All of them have at least 30+ coins. The App calls the API everyminute to update the coins, orders, balances etc.

Everyminute the App makes 396 requests per minute. This can be dropped down to only 6 requests per minute per API key.

Currently it is only possible to get the orders by passing a coin market. For example:

$bitvavo->getOrders("BTC-EUR", [])

When syncing 30 coins+ there will be 30 requests only for retrieving the orders.

Adding an option like retrieving all the account orders will decrease the requests to only 1 for retrieiving orders.

$bitvavo->getAllOrders([]); // returns all the orders by account