Visual Studio Projects: Provide a command line VS build procedure

Similar to the build_ming.bat procedure which will invoke MinGW to
biuild siimulators, this procedure will rebuild all of SIMH simulators using
Visual Studio.

If this procedure is not invoked from a Developer Command Prompt
then the VS2008 tools are preferred if VS2008 is installed,
otherwise the installed Visual Studio tools will be used
prefering newer Visual Studio versions over older ones.

If this procedure is invoked from a Developer Command Prompt
then the tool chain provided with the command prompt is used
to build the simh projects.

A single argument to this procedure may be the word Debug, which
will cause Debug binaries to be build rather than the Release
binaries which is the default.

Visual Studio Projects/0ReadMe_Projects.txt

@@ -26,7 +26,10 @@ For Example, the directory structure should look like:
     .../simh/windows-build/winpcap/WpdPack/Include/pcap.h
     .../simh/windows-build/libSDL/SDL2-2.0.3/include/SDL.h
 
-The contents of the windows-build directory can be downloaded from:
+If you have a command line version of git installed in your environment
+then the windows-build repository will be downloaded and updated 
+automatically.  If not, then the contents of the windows-build directory 
+can be downloaded from:
 
     https://github.com/simh/windows-build/archive/windows-build.zip
 
@@ -61,3 +64,7 @@ If you are using a version of Visual Studio beyond Visual Studio 2008, then
 your later version of Visual Studio will automatically convert the Visual 
 Studio 2008 project files.  You should ignore any warnings produced by the 
 conversion process.
+
+If you have a version of Visual Studio installed and want to build all the
+simulators from a command prompt, the file build_vstudio.bat in the root
+of the simh source tree will do that without any furthur interaction.