Recommendation is to avoid using the year nomenclature as this
information is already encoded in the git repo. Avoids needing to
repeatly update.
Also updates AUTHORS.txt from current repo with contributor names
This is a pretty major rework of the snapping system.
The GRID_HELPERs now have a separate CONSTRUCTION_MANAGER
which handles some of the state involving "construction
geometry".
This is fed with 'extended' geometry (e.g. "infinite" lines from
segments) for use in generating things like intersection points.
It also handles adding this geoemtry to a GAL view item
(CONSTRUCTION_GEOM) for display to the user.
The process is:
* A TOOL creates a GRID_HELPER
* Optionally, it pre-loads a "persistent" batch of construction
geometry (e.g. for an item's original position)
* The grid helper finds useful snap 'anchors' as before, including
those involving the construction items.
* Other items on the board can be 'activated' by snapping to one
of their main points. Then, if it has construction geometry,
it will be added to the display. At most 2 items of this kind of
geometry are shown, plus the original item, to reduce avoid
too much clutter.
The dashed snap lines state machine is also handled in the
CONSTRUCTION_MANAGER and displayed in the CONSTRUCTION_GEOM item.
