Release alpha.18

[axelpale]

Breaking changes:

• all Hyperspace transformations eventually cause Viewport to emit idle, not only pointer interactions.
• remove Group component
• remove Circle alias of Node component
• rename Plane to Space
• rename TransformerComponent as Transformer
• rename ControlComponent as ViewportControl
• rename InteractiveComponent as Interactive
• rename Component:getVector as :createVector
• rename Component:getPoint as :createPoint
• rename Component:getDirection as :createDirection
• remove Component:getRotation alias for :createDirection
• remove tapspace.math (instead install affineplane if needed)
• move Transformer:getScale to Component:getScale

New features:

• Composite component (for a set of components, like Space). Space and Hyperspace inherit from it.
• Hyperspace:rotateBy
• Arc and Edge components are now interactive Items
• Component:createBasis
• Component:createOrientation
• Box:fromBoxes allows Basis in addition to Component
• Node:getBoundingBox (circle shape yields custom boundary)
• Circle:getCollisionArea to compute a degree of collision
• Measurement:areaVisible provides the overlapping area between the target and the viewport.
• Transformer :getDistanceTo and :getVectorTo methods allows Point target

Bugfixes:

• remove hardcoded background color for ZoomControl
• methods that reorder DOM avoid unnecessary work to prevent flicker
• repair Viewport :zoomToFill and :zoomToFit behavior with zero-size targets
• repair Viewport :limitTo behavior with zero-size targets.
• repair inverted KeyboardZoom
• repair Viewport:setOrientation direction
• repair FrameComponent:setSize docs to mention about (w,h) parameters

Other improvements:

• a bit leaner documentation via upgrade to yamdog 2.1.0
• clarified documentation of many methods
• new test utilities: almostEqualBox