Implement commands for management of resident keys

Implement command 0x41 which is used by OpenSSH for reading RKs. It has
the following subcommands:
 * CMD_CRED_METADATA - get number of saved/remaining RKs
 * CMD_RP_BEGIN/CMD_RP_NEXT - iterate over the saved RPs
 * CMD_RK_BEGIN/CMD_RK_NEXT - iterate over the RKs for a given RP

Fixes issue #374 and issue #314

fido2/ctap.h

@@ -17,6 +17,7 @@
 #define CTAP_RESET                  0x07
 #define GET_NEXT_ASSERTION          0x08
 #define CTAP_VENDOR_FIRST           0x40
+#define CTAP_CBOR_CRED_MGMT_PRE     0x41
 #define CTAP_VENDOR_LAST            0xBF
 
 #define MC_clientDataHash         0x01
@@ -37,6 +38,16 @@
 #define GA_pinAuth                0x06
 #define GA_pinProtocol            0x07
 
+#define CM_cmd                    0x01
+    #define CM_cmdMetadata        0x01
+    #define CM_cmdRPBegin         0x02
+    #define CM_cmdRPNext          0x03
+    #define CM_cmdRKBegin         0x04
+    #define CM_cmdRKNext          0x05
+#define CM_rpIdHash               0x02
+#define CM_pinProtocol            0x03
+#define CM_pinAuth                0x04
+
 #define CP_pinProtocol            0x01
 #define CP_subCommand             0x02
     #define CP_cmdGetRetries      0x01
@@ -285,6 +296,16 @@ typedef struct
 
 } CTAP_getAssertion;
 
+typedef struct
+{
+    int cmd;
+    uint8_t rpIdHash[32];
+    uint8_t pinAuth[16];
+    uint8_t pinAuthPresent;
+    int pinProtocol;
+} CTAP_credMgmt;
+
+
 typedef struct
 {
     int pinProtocol;