render activities using HTML links for symbols

[abstratt]

Generate links to referenced operations/symbols when showing blocks of code in the documentation. It would make it navigating the documentation much easier.

[abstratt]

Design idea

Requirements

• preserve the ability to generate pure text
• do not couple generation of text with any specific format
• allow for varying rich text formats, not only HTML

Proposed solution

Generators will allow symbol reference weavers to be provided for a code generation operation. Weavers will be invoked for every action being rendered, and will potentially adorn symbol references as they see fit (generating HTML links, for instance).

[abstratt]

Depends on abstratt/textuml#158