Updated Plupload.csproj to import project successfully in Visual Studio 2012, Readme.md (Flex SDK Download URL updated) and Automatic build for Flash in Windows environment

- Removed `ProjectTypeGuids` and changed `TargetFrameworkVersion` to 4.0 to make it compatible with Visual Studio 2012.
Please remember to install Silverlight 4 SDK (http://www.microsoft.com/en-us/download/details.aspx?id=7335) to import project successfully.
- Flex SDK Download Link updated in Readme.md
- `build.sh` from Linux adapted to Windows, making Flash build much more easier on this platform. If build fails, message is thrown informating user that Java JDK (32-bit) is needed to use mxmlc. It have a link to StackOverflow where are commented how to set JAVA_HOME if compile fails even with Java JDK installed. It verifies if the folder that user have selected is from FLEX SDK. If not, message is thrown and Select dialog back again.
It is a basic script, I hope it can help someone.