The section 9 was extended with the "filter-config" syntax of every
supported filter, but the legacy "filter" directive entries were left
unorganized: the decompression directives were dangling at the end of the
HTTP compression subsection, the "filter-config" entries of the SPOE, cache
and fcgi-app filters were separated from their legacy counterparts, and
the descriptions of the legacy directives were missing or misplaced.
Dedicate a subsection to the decompression filter, renumbering the
following ones, and update the cross-references to the renumbered
sections. Move each "filter-config" entry next to the legacy directive it
supersedes, and the historical note about the HTTP compression move from
the deprecated "filter compression" alias entry to the end of the HTTP
compression subsection. Finally, complete the descriptions of the legacy
"filter" directives and format them like the "filter-config" ones.