Change the prototype of the callback in SKIPDATA option. Suggested by Ben Nagy.

Original prototype:
  typedef size_t (*cs_skipdata_cb_t)(const uint8_t *code, uint64_t offset, void* user_data);

Now we add @code_size argument to reflect the size of the input buffer @code.
Also, we change the data type of @offset to size_t because this argument indicates the
distance from currently examining bytes to @code, but not the address of the byte.

  typedef size_t (*cs_skipdata_cb_t)(const uint8_t *code, size_t code_size, size_t offset, void* user_data);