solution.
Currently, Tix is not built in Debug configuration.
This change also:
- simplifies some Tcl/Tk-related msbuild properties for _tkinter
- copies the Tcl and Tk DLLs into the build output directory, meaning
they will always be available after a build without having to copy
them manually or change PATH
- removes PCbuild/build_tkinter.py: the solution does the build without
needing to invoke Python (so Tcl/Tk/Tix can be built in parallel with
the rest of the build using the `/m` msbuild command line switch)
- removes an outdated README concerning building Tcl/Tk on AMD64
Zachary Ware