Revert incomplete Asciidoc filetype commit.

This reverts commit da78a44a1cfeb753e0d06d7175e882f508ad9788.
Add Asciidoc filetype

Add a filetype for Asciidoc with symbol parser, but not styling.
Correct Names of levels

Make the top level the Document, make lower levels translatable
although they do not normally show in Symbols pane.
Fix indent setting

Asciidoc requires single line comments to be at the start of the line
so do not want indent.
Comment future fixes/additions

Note where Asciidoc features need to be supported that would
prevent code sharing with other markup parsers.