Optimize _Py_hashtable_get() and _Py_hashtable_get_entry() for
pointer keys:
* key_size == sizeof(void*)
* hash_func == _Py_hashtable_hash_ptr
* compare_func == _Py_hashtable_compare_direct
Changes:
* Add get_func and get_entry_func members to _Py_hashtable_t
* Convert _Py_hashtable_get() and _Py_hashtable_get_entry() functions
to static nline functions.
* Add specialized get and get entry for pointer keys.
_Py_hashtable_new() now uses PyMem_Malloc/PyMem_Free allocator by
default, rather than PyMem_RawMalloc/PyMem_RawFree.
PyMem_Malloc is faster than PyMem_RawMalloc for memory blocks smaller
than or equal to 512 bytes.
* Move Modules/hashtable.h to Include/internal/pycore_hashtable.h
* Move Modules/hashtable.c to Python/hashtable.c
* Python is now linked to hashtable.c. _tracemalloc is no longer
linked to hashtable.c. Previously, marshal.c got hashtable.c via
_tracemalloc.c which is built as a builtin module.
