`core/node.coffee`: `_absolute` -> `_transform`
`core/Vector.coffee`: code tweaks
`core/Matrix3.coffee`: multiple bugs fixed

- Missing brackets caused an invalid value for `@_values`.
- 2 reference bugs fixed
`core/Matrix3.coffee`: return value bug fixed

`multiply` returns the matrix object now. This fixes the `_update()`
method in `core/Node.coffee`,
`core/Node.coffee`: multiple bugs fixed

- reference bug fixed
- `update` aborts now if there is no `@_parent`. Previously,
`canvas.update()` failed because a `Canvas` object has no `_parent`.
`core/Canvas.coffee`: matrix bug fixed

Since a `Canvas` object is the root node of the scene graph, its
transformation matrix will never change, representing a position of
`new Vector 0, 0` and a rotation of `0`. The resulting matrix is the
neutral unit matrix.

The implementation of `_update` prevents `Node._update` from being
called.
`core/Block.coffee`: multiple bugs fixed

- `Node.constructor` has to be called *after* `@children` is
initialized.
- Updated `add` and `remove` to use the setter method `parent`.
`shapes/deps.coffee`: fixed missing `Vector` dep.
`shapes/Point.coffee`: whitespace tweaks

+readability
`util/Interval.coffee`: multiple bugs fixed

- `constructor`: reference bug fixed
- `_callback` scope & call fixed
tweaked return value -> smaller `/dist` files
`util/Rendering.coffee`: multiple bugs fixed
`module.exports` files -> smaller `/dist` files

A dedicated file for all `module.exports` of a module reduces the
distribution file size.
properties as comments -> smaller `/dist` files

Replacing placeholder instance properties in classes by comments
greatly reduces the file size.