Added ProcessEnvironment BuildServer

This pull is a discussion. I quickly spicked a build server implementation which sets environment variables in the executing process. The idea was that a build script which calls msbuild and compiles a solution which contains projects with the gitflowversiontask the environment variables could be read by the script. Unfortunately I couldn't read the environment variable in my scripts. 

Any ideas how this could be improved? Is this useful or not? Is there a better and working approach to feed information back into the build script without calling GitFlowVersion.exe manually?