Correct ARM64 SIZE_OF_JMP from 8 to 16 and spell out 2*4 as 8. (#11)

This is a lot of bytes to overwrite, and it precludes
patching a number of small-ish functions, but it is how many.

For example, automatic following imports, has lead to system service stubs,
that were smaller than this (and aligned less than this).

src/detours.cpp

@@ -893,7 +893,7 @@ struct _DETOUR_TRAMPOLINE
 C_ASSERT(sizeof(_DETOUR_TRAMPOLINE) == 120);
 
 enum {
-    SIZE_OF_JMP = 8
+    SIZE_OF_JMP = 16
 };
 
 inline ULONG fetch_opcode(PBYTE pbCode)
@@ -915,7 +915,7 @@ PBYTE detour_gen_jmp_immediate(PBYTE pbCode, PBYTE *ppPool, PBYTE pbJmpVal)
         pbLiteral = *ppPool;
     }
     else {
-        pbLiteral = pbCode + 2*4;
+        pbLiteral = pbCode + 8;
     }
 
     *((PBYTE*&)pbLiteral) = pbJmpVal;