Initial changes for TCL 9.0.

Fixed package requires to work with TCL 9.0.
Removed obsolete macro _ANSI_ARGS_, use ANSI arg definitions, etc.
Macros: CONST84 to const, WIN32 to _WIN32, CONST to const, VOID to void, etc.
Replaced Tcl_SaveResult with Tcl_SaveInterpState, Tcl_RestoreResult with Tcl_RestoreInterpState, and Tcl_DiscardResult with Tcl_DiscardInterpState.
Use Tcl_BackgroundError for pre TCL 8.6 and Tcl_BackgroundException for TCL 8.6+.