Globally unique node identifiers

[edwardchalstrey1]

Requested enahancement or feature

Suggestion from Bernhard email:

A main change in specification for the .ef format, which I would promote, would be to separate levels and node identifiers. Default for the levels is currently 0,2,4, etc. which are vertical distance in centimeters downwards from the root. Levels have dual functions as vertical coordinates (always rounded to three decimal places in case of longer decimal fractions) and identifiers for nodes. Nodes are identified as pairs of the form level,id
where id can be any identifier, such as x or abc012 (usually integers). But this requires re-naming nodes (easily done by substitution, but still) whenever their level is changed for layout purposes. So I would just give globally unique node identifiers instead.

[edwardchalstrey1]

Note: if we update the .ef format here, we'll want to also update .ef files produced by GTE to match this new specification.

TODO:

• Move existing specs.pdf into a markdown document
• Open a new branch with changes to the spec documented
• Update code and examples with this change, merge to main branch in draw_tree
• Ensure GTE can also create new file format