Allow access to MS-Windows Registry from Lisp programs

Allow access to MS-Windows Registry from Lisp programs

* src/w32.c (g_b_init_reg_open_key_ex_w)
(g_b_init_reg_query_value_ex_w)
(g_b_init_expand_environment_strings_w): New init flags.
(globals_of_w32): Initialize them at startup.
(RegOpenKeyExW_Proc, RegQueryValueExW_Proc)
(ExpandEnvironmentStringsW_Proc): New function typedefs.
(reg_open_key_ex_w, reg_query_value_ex_w)
(expand_environment_strings_w): New wrapper function.
(w32_read_registry): New function.
* src/w32fns.c (Fw32_read_registry) [WINDOWSNT]: New primitive.
(syms_of_w32fns) [WINDOWSNT]: Defsubr it.  DEFSYM "HKLM", "HKCU",
etc. root keys.

* etc/NEWS: Mention the new primitive.