Adds explicit titles to documentation index.
Adds documentation sections to the index.
Splits index into documents and APIs.
Moves TOC index entry generation to rstgen module.

We want it there so that index entries appear in the same order as they
are found in the input text.
Picks the correct symbol text for theindex embedded tocs.
Refactors adhoc table of sequences into TIndexedDocs type.
Generates quick jump list to documentation files.
Generates quick jump list to modules.
Indexes tocs of documents even if they don't show any.
Updates some document titles to read better in the index.
Removes many fake `idx` entries.

These *fake* entries are not needed any more now that the table of
contents of documentation files appear in the index.
Links naming api with coding guidelines.
Fixes repeated index terms leading to same HTML anchor.

Instead of a hash for the rst node tree (which will always be the same)
a simple counter table is used.
Fixes title and subtitle not setting the current section.
Adds abstypes.txt to list of documentation to build.
Reduces length of lines to remove compilation warnings.
Assigns default title to module documentation.
Removes text TOCs from the symbol index.
Inserts the title index term at the beginning of the buffer.
Adds documentation section about the idx file format.