Adds support for Tcl 9

[apnadkarni]

This PR adds support for Tcl 9 and along the way fixes some potential buffer overflows. Demos are functional but before accepting the pull request, you may want to consider the following:

• Only Windows code modified except for Tcl scripts where use of the encoding commands was changed so the replace profile is in effect instead of Tcl 9 default strict mode.
• Non-Unicode builds (_MBCS) not tested and probably will not work. In any case, I do not believe _MBCS will fully work with modern Tcl versions and are completely unnecessary for the NT platform. Win98 is long dead.
• A TIP 477 nmake based build system has been added, partly to match conventions in other extensions but mostly because I could not get the cmake builds to work with Tcl 9 installations. All tests done using this nmake build config. Requires Tcl 8.6.8 or later to build. The existing cmake build continue to work with this PR with 8.6.
• Tested with the demos scripts on Win 10 (Tcl 8.6 and 9.0.0 with both x86 and x64.) Not tested with earlier versions of Tcl (8.4/8.5)
• Version is not changed but probably should be since _MBCS is no longer supported