multi-layer rendering, time control, and component base type

The release adds methods for controlling time, improvements to multi-layer rendering, fixes for a number of core methods, and in addition cleans up the base class hierarchy.

Components renamed:

• Field is now the name for what used to be Plane, the basic unit of drawing, a 2d structure of 8-bit values
• Scroll is now used instead of Camera

Time control:

• ra.pause to pause the flow of time
• framerate is automatically limited to 60fps on high refresh monitors
• --tick flag for command-line allows rendering at a specific ra.tick value

Layering:

• any layer can be scrolled or use tilesets
• rendering semantics cleaned up for multi-layer scenes
• --save flag supports multiple layers
• setComponent can be used on any layer to bank switch components

Add-on features:

• TilesetBuilder is a display that saves rendered frames to a tileset
• inspector can be used to capture rendering data (web only)
• dipchange event
• contrib tool for importing "Tiled" projects

Various methods added:

• Tile.xform which is the same as Field.xform
• Polygon.resize will scale up or down polygon objects
• Field.toArrays instead of Field.pack, mainly used for tests