2.0.0

• Fixes a type level error in Mapbox.Expression.step that made it useless.
• Relaxes some types in preparation for mapbox 0.49
• Adds a very early version of a style spec generator

Full diff:

---- Mapbox.Expression - MAJOR ----

    Changed:
      - step :
            Expression exprType2 Float
            -> List ( Float, Expression exprType1 output )
            -> Expression exprType1 output
            -> Expression exprType2 output
      + step :
            Expression exprType1 output
            -> List ( Float, Expression exprType1 output )
            -> Expression exprType2 Float
            -> Expression exprType2 output
    


---- Mapbox.Layer - MAJOR ----

    Changed:
      - backgroundPattern :
            Expression CameraExpression String -> LayerAttr Background
      + backgroundPattern :
            Expression any String -> LayerAttr Background
    
      - fillExtrusionPattern :
            Expression CameraExpression String -> LayerAttr FillExtrusion
      + fillExtrusionPattern :
            Expression any String -> LayerAttr FillExtrusion
    
      - fillPattern : Expression CameraExpression String -> LayerAttr Fill
      + fillPattern : Expression any String -> LayerAttr Fill
    
      - linePattern : Expression CameraExpression String -> LayerAttr Line
      + linePattern : Expression any String -> LayerAttr Line