input: Write a python function to initialize and configure the GridWorld environment.
  assert standard_grid().rows == 3
  assert standard_grid().cols == 4
  assert standard_grid().current_state() == (2, 0)
  assert standard_grid().rewards == {(0, 3): 1, (1, 3): -1}
  assert standard_grid().actions == {
      (0, 0): ('D', 'R'),
      (0, 1): ('L', 'R'),
      (0, 2): ('L', 'D', 'R'),
      (1, 0): ('U', 'D'),
      (1, 2): ('U', 'D', 'R'),
      (2, 0): ('U', 'R'),
      (2, 1): ('L', 'R'),
      (2, 2): ('L', 'R', 'U'),
      (2, 3): ('L', 'U'),
  }
output: def standard_grid():
      class Grid:
          def __init__(self, rows, cols, start):
              self.rows = rows
              self.cols = cols
              self.i = start[0]
              self.j = start[1]
  
          def set(self, rewards, actions):
              self.rewards = rewards
              self.actions = actions
  
          def current_state(self):
              return (self.i, self.j)
  
      g = Grid(3, 4, (2, 0))
      rewards = {(0, 3): 1, (1, 3): -1}
      actions = {
          (0, 0): ('D', 'R'),
          (0, 1): ('L', 'R'),
          (0, 2): ('L', 'D', 'R'),
          (1, 0): ('U', 'D'),
          (1, 2): ('U', 'D', 'R'),
          (2, 0): ('U', 'R'),
          (2, 1): ('L', 'R'),
          (2, 2): ('L', 'R', 'U'),
          (2, 3): ('L', 'U'),
      }
      g.set(rewards, actions)
      return g