Improve the documenter (documentation generator)

[fmease]

General

• Rewrite the documenter to render pages in parallel (without creating files yet)
• Filter non-public bindings by default
• Show bindings of any visibility with --show-private-declarations, -P (placeholder name) and also render the public attribute (with a link to the exposure reach if restricted). Should this apply to dependencies as well?
• Generate documentation for re-exports (public use-bindings). Which use-bindings should we show with --show-private-declarations? Also @(public topmost) for example?
• remove the debug attribute output in the documenter (at last!) and implement proper attribute support (except public)
• Make doc an attribute namespace and make doc-* attributes members of the namespace (stripped off their prefix) (superseded by Remove @doc-{reserved-identifier{s,},attribute{s,}} and everything in core annotated with it #131)
• Consider merging @doc-attributes, @doc-attribute, @doc-reserved-identifiers, @doc-reserved-identifier into a more general @doc-role/@doc.role (superseded by Remove @doc-{reserved-identifier{s,},attribute{s,}} and everything in core annotated with it #131)
• For types and functions, format parameters in the "sugared form" (not as part of pi-type literals). Allow the user to change between both formats. Either per declaration (but I don't want to add a noisy/cluttered link/button) or in the settings (see other bullet points)
• If deemed useful, implement a settings button (maybe on the ledge on the right) where one can set the theme, etc.
• Implement a dark theme and manually switching between light, dark and system (where the latter automatically sets the appropriate theme)
• Search for good color palettes and commit to it. Note that we don't use that many colors right now (which is good) except for certain special attributes (deprecated, internal, …)
• Somehow add the label internal to internal attributes. Parse the name of the attribute given with @doc-attribute (…) and check if it is internal (but is_internal is a method on AttributeKind not AttributeName!)
• Make the argument of @doc-attribute (…) a path instead of a text literal (superseded by Remove @doc-{reserved-identifier{s,},attribute{s,}} and everything in core annotated with it #131)
• Create an unstable option -Z developing (…) which replaces the const DEVELOPING
• Do not generate (dead) links to bindings defined in an external component (e.g. core) that is not part of the documentation pipeline (because of --no-deps or --no-core/no core: {} (e.g. linking Type to reserved.html and attributes))
• Do not generate (dead) links to private bindings (once we don't show private bindings)
• UI test suite

Searching

• Implement proper searching based on Levenshtein distance
  • Find a JS implementation with a good license
  • Don't treat paths as a string but as separate segments without losing the power of Levenshtein distances
• If feasible create a single search index file which contains information about all documented components
• If deemed useful, search through all packages/components or only the goal (or the current?) component depending on a setting
• Make the search results pop up while typing (though throttled)
• Show the type of the search result next to the path (normal declaration, keyword, attribute, …)
• If deemed necessary, show the start of the documentation next to the path
• The list of results should close when clicking outside of the search bar or the search results
• If possible optimize the search index for lookup speed
• Actually fully evaluate the type signatures
• Public expressions (esp. "type aliases") should be treated as neutrals/should be irreducible. This requires a separate function in the typer I suppose. This strongly ties in with irreducible opaque (non-@transparent) bindings (see Opaque by default (aka abstract by default) #115)

AsciiDoc(tor) Integration

• Pass documentation to AsciiDoctor with the flag -Z asciidoc (…) (via af2ecec) (note: this is not performant at all (see description of 2cd1401 for more); we need our own AsciiDoc processor implementation)
• Somehow support using binding paths in AsciiDoc (as a (pseudo) macro?) (via 2cd1401)
• Implement --opening of the documentation using the default browser (via 9ceeddb)
• Write a static source code highlighter and integrate it
• Try to get rid of the dependency on AsciiDoctor (low priority, high cost)

Source File View

• Generate source file pages for each source file
• Allow linking to a range of lines
• Set the proper URL for source code links
• Also render a source link for modules (we only do that for types and functions, right now)

Fonts

• Convert all TTF into WOFF and WOFF2 files (with the extension .ttf.woff/.ttf.woff2) and update fonts.css
• Make sure the licenses are set up correctly