Add packet/payload matching to WinDivert (#156).

Adds the follow terms to the filter language:
- packet[idx]: 8bit packet value at idx.
- packet16[idx]: 16bit packet value at idx.
- packet32[idx]: 32bit packet value at idx.
- PROTO.Payload[idx]: 8bit payload value at idx.
- PROTO.Payload16[idx]: 16bit payload value at
  idx.
- PROTO.Payload32[idx]: 32bit payload value at
  idx.
where PROTO is {tcp,udp}.

16 and 32bit values assume network byte ordering.

The index may be:
- An undecorated integer, in which case the
  packet or payload is treated as a 8/16/32bit
  value array, similar to C arrays.
- A 'b' decorated integer, (e.g, packet32[17b]),
  in which case the integer is interpreted as a
  byte offset.
- A negative (un)decorated integer, in which
  case indexing begins at the *end* of the
  packet or payload.  E.g., packet32[-1] is the
  last 32bits of the packet.

If the index is out-of-bounds, then the test
is deemed to be equivalent to "false".

include/windivert_device.h

@@ -127,8 +127,17 @@
 #define WINDIVERT_FILTER_FIELD_PROTOCOL             65
 #define WINDIVERT_FILTER_FIELD_LAYER                66
 #define WINDIVERT_FILTER_FIELD_EVENT                67
+#define WINDIVERT_FILTER_FIELD_PACKET               68
+#define WINDIVERT_FILTER_FIELD_PACKET16             69
+#define WINDIVERT_FILTER_FIELD_PACKET32             70
+#define WINDIVERT_FILTER_FIELD_TCP_PAYLOAD          71
+#define WINDIVERT_FILTER_FIELD_TCP_PAYLOAD16        72
+#define WINDIVERT_FILTER_FIELD_TCP_PAYLOAD32        73
+#define WINDIVERT_FILTER_FIELD_UDP_PAYLOAD          74
+#define WINDIVERT_FILTER_FIELD_UDP_PAYLOAD16        75
+#define WINDIVERT_FILTER_FIELD_UDP_PAYLOAD32        76
 #define WINDIVERT_FILTER_FIELD_MAX                  \
-    WINDIVERT_FILTER_FIELD_EVENT
+    WINDIVERT_FILTER_FIELD_UDP_PAYLOAD32
 
 #define WINDIVERT_FILTER_TEST_EQ                    0
 #define WINDIVERT_FILTER_TEST_NEQ                   1