Updated Readme.md (Flex SDK URL)
Update Plupload.csproj

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.
Automate Flash build

Linux is not the only one who deserves make build process a bit easier.
It is a Script that have a File Dialog to select Flex SDK folder and shows
friendly message error if compilation fails. (In most cases it fails because Java JDK is ausent or JAVA_HOME problems).
Complement to build.vbs

`mxmlc` is a too long line to be called from VBScript directly. The solution that I have found
was creating an external bat file that call the file.
VBScript do not read it response, but check if the file was created successfully.
If the file not exist, error message is thrown in VBScript.
The BAT is not closed automatically to allow user to read mxmlc output in prompt.