Add default case to switch statements

[kaidesu]

What does this implement or fix?

Added

• Added ability to define a default case to switch statements
• Added parser tests for switch statements

switch(value) {
  case true {
    // handle true case
  }

  case false {
    // handle false case
  }

  default {
    // handle default case
  }
}

Additional Notes

Thanks to @skx and skx/monkey#71 for an example on an implementation 👍🏻