Add the ability to execute subprocesses asynchronously

[adityarao2005]

We'll have to look into how to do this using C++ language features but it should include the following:

• Setting the working directory of the subprocess
• Setting the environment variables of the subprocess
• Being able to redirect input, output, and error of the subprocess
• Also being able to read and write from the subprocess
• View the error code of the subprocess
  All of this should be supported using our inbuilt task API.