Remove automatic discovery in NimBLEClient::connect().

Instead of discovering the peripheral database on connection and consuming
the associated resources this will give the user more control over the
discovery operation.

* Adds void NimBLEClient::discoverAtrributes() for the user to discover all
the peripheral attributes as a replacement for the former functionality.

* getServices(), getCharacteristics(), getDescriptors() now take an
optional bool parameter (default false).
If true it will clear the respective vector and retrieve all the respective
attributes from the peripheral. If false it will retrieve the attributes
only if the vector is empty, otherwise the vector is returned with the
currently stored attributes.

* getService(NimBLEUUID), getCharacteristic(NimBLEUUID), getDescriptor(NimBLEUUID)
will now check the respective vectors for the attribute object and, if not
found, will retrieve (only) the specified attribute from the peripheral.

API_DIFFERENCES.md

@@ -122,6 +122,35 @@ Has been removed from the API as it is no longer maintained in the library.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.   
 
+**NEW** on May 23, 2020
+> ```
+> NimBLEClient::getServices(bool refresh = false)   
+> NimBLERemoteService::getCharacteristics(bool refresh = false)   
+> NimBLERemoteCharacteristic::getDecriptors(bool refresh = false)
+>```
+> These methods now take an optional (bool) parameter.   
+If true it will clear the respective vector and retrieve all the respective attributes from the peripheral.   
+If false it will retrieve the attributes only if the vector is empty, otherwise the vector is returned   
+with the currently stored attributes.   
+
+> Removed the automatic discovery of all peripheral attributes as they consumed time and resources for data   
+the user may not be interested in.   
+   
+> Added `NimBLEClient::discoverAtrributes()` for the user to discover all the peripheral attributes   
+to replace the the former functionality.
+   
+   
+> ```
+>getService(NimBLEUUID)   
+>getCharacteristic(NimBLEUUID)   
+>getDescriptor(NimBLEUUID)
+>```
+>These methods will now check the respective vectors for the attribute object and, if not found, will retrieve (only)   
+the specified attribute from the peripheral.
+
+> These changes allow more control for the user to manage the resources used for the attributes.   
+
+
 #### 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.