Breaking: Use std::vector instead of std::map in client classes (#46)

* Exchange map for vector, saving 1,076 bytes of program memory and 5,024 bytes of heap for a small device (LYWSD03MMC)

* Removing m_characteristicMapByHandle (using the handles form m_characteristicVector instead) saving in total (compared to the current master) 1,508 bytes of program memory and 6,500 bytes of heap for a small device (LYWSD03MMC)

* Change NimBLEScan container from std::map to std::vector

* Add function to get advertised device by address

* Update documentation

API_DIFFERENCES.md

@@ -100,7 +100,7 @@ The `BLEAdvertisedDeviceCallbacks` class `onResult()` method now receives a poin
 Defined as:
 ```
 bool connect(NimBLEAdvertisedDevice* device, bool refreshServices = true);
-bool connect(NimBLEAddress address, uint8_t type = BLE_ADDR_TYPE_PUBLIC, bool refreshServices = true);
+bool connect(NimBLEAddress address, uint8_t type = BLE_ADDR_PUBLIC, bool refreshServices = true);
 ```
 If set to false the client will use the services database it retrieved from the peripheral last time it connected.    
 This allows for faster connections and power saving if the devices just dropped connection and want to reconnect.
@@ -111,6 +111,17 @@ NimBLERemoteCharacteristic::registerForNotify();
 ```
 Now return true or false to indicate success or failure so you can choose to disconnect or try again.
 
+```
+NimBLEClient::getServices()   
+NimBLERemoteService::getCharacteristics()
+```
+Now return a pointer to a `std::vector` of the respective object database instead of `std::map`.
+
+`NimBLERemoteService::getCharacteristicsByHandle()`
+Has been removed from the API as it is no longer maintained in the library.   
+
+The last two above changes reduce the heap usage significantly with minimal application code adjustments.   
+
 #### Client Security:
 The client will automatically initiate security when the peripheral responds that it's required.    
 The default configuration will use "just-works" pairing with no bonding, if you wish to enable bonding see below.