text: Title: Enhanced object creation, using column references
  Body: When instantiating a Table object, we do this (like in 99% of ORMs):
  
  ```python
  Band(name="Pythonistas", popularity=1000)
  ```
  
  Some Piccolo queries allow you to pass in a dictionary mapping column references to values, instead of using kwargs. It's nice for tab completion, and also for catching errors.
  
  ```python
  Band.update({
      Band.popularity: 2000
  }).run_sync()
  ```
  
  It would be good to have this ability for instantiating objects too. Something like:
  
  ```python
  Band(_data={Band.name: "Pythonistas", Band.popularity: 2000})
  ```