string with the process' command line; arguments that have embedded whitespace must be enclosed in inside double-quotes ("). Note: The class will use only slices, .dup when necessary.
associative array of strings with the process' environment variables; the variable name must be the key of each entry.
char[] command = "myprogram \"first argument\" second third"; char[][char[]] env; // Environment variables env["MYVAR1"] = "first"; env["MYVAR2"] = "second"; auto p = new Process(command, env)
Constructor.