Implement a filter compiler with new features.

Replaces the old filter compiler with a new version that:
- Is a cleaner, more extensible, implementation.
- Can report specific error messages (e.g. bad token vs parse error).
- Supports the new C-style if-then-else expression "(A? B: C)" syntax.

Two new WinDivert helper API functions have been implemented:
- WinDivertHelperCheckFilter() can be used to check a filter string for
  errors.
- WinDivertHelperEvalFilter() evaluates a filter on a given packet.  Will be
  useful for testing.

include/windivert.h

@@ -352,6 +352,24 @@ extern WINDIVERTEXPORT UINT WinDivertHelperCalcChecksums(
     __in        UINT packetLen,
     __in        UINT64 flags);
 
+/*
+ * Check the given filter string.
+ */
+extern WINDIVERTEXPORT BOOL WinDivertHelperCheckFilter(
+    __in        const char *filter,
+    __in        WINDIVERT_LAYER layer,
+    __out_opt   const char **errorStr,
+    __out_opt   UINT *errorPos);
+
+/*
+ * Evaluate the given filter string.
+ */
+extern WINDIVERTEXPORT BOOL WinDivertHelperEvalFilter(
+    __in        const char *filter,
+    __in        WINDIVERT_LAYER layer,
+    __in        PVOID pPacket,
+    __in        UINT packetLen,
+    __in        PWINDIVERT_ADDRESS pAddr);
 
 /****************************************************************************/
 /* WINDIVERT LEGACY API                                                     */