Numerous updates to the P4Win project files.
* P4EnvVariables.props now sets SDKs, P4API_DIR, OPENSSL_DIR variables to paths relative to the directory containing the P4EnvVariables.props file.
* Removed the non-Unicode configurations.
* They are compatible with the following versions of Visual Studio: 2010, 2012, and 2013. Note that since a Visual Studio 2013 compatible version of P4API is not yet available, P4Win will not build with Visual Studio 2013.
* The common controls manifest is now added via project file settings instead of via P4win.rc. This is necessary because using the RC file causes errors in Visual Studio 2012 and Visual Studio 2013.
* Modified the P4Win project so that it links with OpenSSL. This is necessary in order to fixed unresolved external symbol errors when linking. Apparently the latest version of the P4API libraries depend on OpenSSL.
* Previously certain compiler options were pointlessly set for each CPP file in the P4Win project instead of simply being set at a project level basis. This makes changing compiler options for all files needlessly difficult. Now all compiler options are set project wide and not on a per file basis.
* Added filters files.
* Added x64 project configurations in preparation for porting P4Win to the x64 platform.