Add connection info class and access methods to server and client.

This adds the ability to access information about the current connection.
A new class was created to wrap the struct ble_gap_conn_desc with methods to retrieve the connection information.

Example server use:
```
for(auto i=0; i<pServer->getConnectedCount();i++) {
    NimBLEConnInfo connInfo = pServer->getPeerInfo(i);
    printf("Connected client %d info:\n", i);
    printf("Peer address: %s\n", connInfo.getAddress().toString().c_str());
    printf("Peer ID address: %s\n", connInfo.getIdAddress().toString().c_str());
    printf("Handle: %u\n", connInfo.getConnHandle());
    printf("Interval: %u\n", connInfo.getConnInterval());
    printf("Timeout: %u\n", connInfo.getConnTimeout());
    printf("Latency: %u\n", connInfo.getConnLatency());
    printf("MTU: %u\n", connInfo.getMTU());
    printf("Master: %s\n", connInfo.isMaster()? "true":"false");
    printf("Slave: %s\n", connInfo.isSlave()? "true":"false");
    printf("Bonded: %s\n", connInfo.isBonded()? "true":"false");
    printf("Authenticated: %s\n", connInfo.isAuthenticated()? "true":"false");
    printf("Encrypted: %s\n", connInfo.isEncrypted()? "true":"false");
    printf("Encryption Key Size: %u\n", connInfo.getSecKeySize());
}
```

Example client use:
```
if (pClient->isConnected()) {
    NimBLEConnInfo connInfo = pClient->getConnInfo();
    printf("Connection info:\n");
    printf("Peer address: %s\n", connInfo.getAddress().toString().c_str());
    printf("Peer ID address: %s\n", connInfo.getIdAddress().toString().c_str());
    printf("Handle: %u\n", connInfo.getConnHandle());
    printf("Interval: %u\n", connInfo.getConnInterval());
    printf("Timeout: %u\n", connInfo.getConnTimeout());
    printf("Latency: %u\n", connInfo.getConnLatency());
    printf("MTU: %u\n", connInfo.getMTU());
    printf("Master: %s\n", connInfo.isMaster()? "true":"false");
    printf("Slave: %s\n", connInfo.isSlave()? "true":"false");
    printf("Bonded: %s\n", connInfo.isBonded()? "true":"false");
    printf("Authenticated: %s\n", connInfo.isAuthenticated()? "true":"false");
    printf("Encrypted: %s\n", connInfo.isEncrypted()? "true":"false");
    printf("Encryption Key Size: %u\n", connInfo.getSecKeySize());
}
```

src/NimBLEClient.h

@@ -23,6 +23,7 @@
 #include "NimBLEAddress.h"
 #include "NimBLEUUID.h"
 #include "NimBLEUtils.h"
+#include "NimBLEConnInfo.h"
 #include "NimBLEAdvertisedDevice.h"
 #include "NimBLERemoteService.h"
 
@@ -71,6 +72,7 @@ public:
     void                                        updateConnParams(uint16_t minInterval, uint16_t maxInterval,
                                                                  uint16_t latency, uint16_t timeout);
     void                                        discoverAttributes();
+    NimBLEConnInfo                              getConnInfo();
 
 private:
     NimBLEClient(const NimBLEAddress &peerAddress);