Allow providing extra arguments in the task definition

[geoffxy]

It would help to be able to declare arguments that should be passed to the executable in a run_experiment() and run_command() as part of the task definition in the COND file. This is because certain experiments may require many arguments and it is tedious to either (i) create a separate script for each instance, or (ii) tack them on to the run argument (making it really long).

For example

run_experiment(
  name="benchmark",
  run="./run_benchmark.sh",
  args={
    memory: "2G",
    threads: "3",
  },
)

would translate to running ./run_benchmark.sh --memory=2G --threads=3.

[geoffxy]

It would be useful if these arguments were also serialized and stored with the task output (may be useful for later processing tasks).