v0.1.9

• Bump version.

• Wait for order status to leave pending state.

• Config: replace minimum_cushion with margin_usage.

  I found the concept of maintaining a minimum cushion to be too hard to
  reason about, and it didn't properly reflect margin usage in a way that
  made sense to me.

  Thus, I've replaced it with margin_usage, which allows you to specify
  how much margin to use as a factor of the net liquidation value. I find
  this to be much better.

• Update thetagang.toml