Blueprint anchors

Background: intended to use "#" as the markup for anchors, using "[[#name]]" or "[[page#name]]" as link to that anchor. Since "#" was reserved for anchors, we opted to use "@" for tags (as recommended in GTD book).

Progressive insight: "#" is most common marker for tags / labels in many SW tools now. Regular users will recognize it as such while the use of "#" for anchors is a more technical use only known to technical users.

Intended way forward: allow both "@" and "#" for tags / labels. Allow customers to use semantics like "@location" and "#topic". (Maybe make it a setting to distinguish these types vs using them intermixed?)

Consequences for anchors: need another representation for anchors. (Some) Mediawiki use syntax like "{{anchor|name}}" and ref like "[[#name]]". This basically means that anchors are considered a kind of special object. We could use object syntax as well, which makes sense as anchors are usually an object property.

So we need a way to set a "name" or "id" property on headings, images and inline objects. For object syntax this is can be explicit property. For headings it can be implicit based on heading text or explicit with special code. Propose something like "{{name=...}}" as a kind of empty object that sets properties for the heading.