Document ranges highlighters

They were not, as pointed out in #736

README.asciidoc

@@ -816,6 +816,9 @@ Options are typed, their type can be
  * `{int,str}-list`: a list, elements are separated by a colon (:)
   if an element needs to contain a colon, it can be escaped with a
   backslash.
+ * `range-faces`: a list, elements are separated by a colon (:), of
+  a buffer range (<begin line>.<begin column>,<end line>.<end column>)
+  and a face (separated by `|`)
  * `enum(value1|value2|...)`: an enum, taking on of the given values
  * `flags(value1|value2|...)`: a set of flags, taking a combination
    of the given values joined by `|`.
@@ -1160,6 +1163,7 @@ general highlighters are:
        -separator switch one can specify a string to separate the line numbers column with
        the rest of the buffer, default is `|`.
  * `fill <face>`: fill using given face, mostly useful with <<regions-highlighters,Regions highlighters>>
+ * `ranges <option_name>`: use the data in the range-faces option of the given name to highlight the buffer.
 
 Highlighting Groups
 ^^^^^^^^^^^^^^^^^^^

doc/manpages/highlighters.asciidoc

@@ -64,6 +64,10 @@ General highlighters
 		specify a string to separate the line numbers column with
 		the rest of the buffer (default is '|')
 
+*ranges* <option_name>::
+	use the data in the range-faces option of the given name to highlight
+	the buffer.
+
 *fill* <face>::
 	fill using the given *face*, mostly useful with regions highlighters
 

doc/manpages/options.asciidoc

@@ -22,6 +22,10 @@ Types
 	a list, elements are separated by a colon (:) if an element needs
 	to contain a colon, it can be escaped
 	with a backslash
+*range-faces*::
+	a list, elements are separated by a colon (:), of pairs of buffer
+	range (`<begin line>.<begin column>,<end line>.<end column>`) and
+	face (separated by `|`)
 *enum(value1|value2|...)*::
 	an enum, taking one of the given values
 *flags(value1|value2|...)*::