Access all environment variables using a simple hash map.

This is a modified version of pull request #13, which I closed after seeing the error in putting in the EnvInject plugin dependency. Here is what my version will accomplish:

-Sets a hash map named "environment" that contains all of the environmental variables. This makes the process of getting variables more simple. (No EnvInject dependency)

-Added into the help file how to use the environment hash map.

You'd better to use `envVars` you've got in the constructor.
Or you don't need `envVars`.