Fixed building of Docs project on Windows

When we try to build Docs on Windows it gives an error for conf.py file. To fix this issue I have created an vb script which will do the following things 

• Read the version from pgadmin/include/version.h
• Copy the en_US/conf.py.in file as en_US/conf.py
• Replace the Long and Short version in conf.py file

Along with that I have also added a prebuild rule to the docs VC++ project. Attached is the patch file.

Please review it and if it sounds good to you than commit it.   
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