Link elements to documentation pages

[naturallymitchell]

When generating an svg image as part of a handbook, it would be really nice to deep link into the handbook from the source code diagram elements.

[adjivas]

@mitchtbaum: There are two limitations:

• The Graphviz's DOT language includes only one URL's attribute by label, so a node can't have more than one link as you can see from this example:

digraph ml {
    ndRelation[URL="https://adjivas.github.io/ml/mml/core/item/relation/enum.Relation.html", label="{<<<Enumeration>>>\nRelation|Association\nAggregation\nComposition\nRealization\nDependency\nNone|+ as_style(&self) -> ArrowShape}"][shape="record"];
}

• The dot crates not implement the URL attribute.

And a question: this rust's comment //! ![uml](ml.svg) is translated by the rustdoc project into <img src="ml.svg" alt="uml">, both text and link from an img's tag are unelectable.

[naturallymitchell]

@adjivas: dot's limits prompted me to open #5 as a way around rust-dot, then seeing this SVG Comparison of Pyramids now lead me to believe that dot only helps with one group of side use cases and that SVG fits the primary use case, documentation. If generating it using an intermediary diagramming/graphing library still makes the most sense, then I believe Dia has the expressiveness and interfaces needed.