Add internal decorator to Stack class

This class won't be exposed at the module level.

Author: rushter

selectolax/modest/node.pxi

@@ -11,6 +11,7 @@ DEF _ENCODING = 'UTF-8'
 
 
 @cython.final
+@cython.internal
 cdef class Stack:
     def __cinit__(self, size_t capacity=25):
         self.capacity = capacity