doc: Add the new grears.matcher features to the lone example.

This isn't really intended to be used outside of the object rules.

tests/examples/text/gears/matcher/default.lua

@@ -11,7 +11,8 @@ local gears = {matcher = require("gears.matcher")} --DOC_HIDE
     -- This rule will match
     local rule1 = {
         rule = {
-            answer = 42,
+            answer     = 42,
+            everything = true,
         },
         properties = {
             name = "baz",
@@ -69,6 +70,41 @@ local gears = {matcher = require("gears.matcher")} --DOC_HIDE
     -- This will add the `rules` to this matcher.
     matcher:add_matching_rules("second", rules, {"first"}, {})
 
+--DOC_NEWLINE
+    -- Some properties cannot be checked with the `==` operator (like those
+    -- with multiple possible types). In that case, it is possible to define
+    -- special comparator function.
+    matcher:add_property_matcher("everything", function(obj, value)
+        return value and obj.answer == 42
+    end)
+
+--DOC_NEWLINE
+
+    -- The same can be done for the property section.
+    matcher:add_property_setter("multiply_by", function(obj, value)
+        obj.answer = (obj.answer or 1) * value
+    end)
+
+--DOC_NEWLINE
+
+    -- It is possible to append rules to existing (or new) sources.
+    matcher:append_rule( "second", {
+        id   = "rule_with_id",
+        rule = {
+            has_elite = true,
+        },
+        properties = {
+            multiply_by = "1337",
+        },
+    })
+
+--DOC_NEWLINE
+
+    -- Or remove them.
+    local rm3 = --DOC_HIDE
+    matcher:remove_rule("second", "rule_with_id")
+    assert(rm3) --DOC_HIDE
+
 --DOC_NEWLINE
 
     -- Apply the properties to `o`
@@ -76,5 +112,12 @@ local gears = {matcher = require("gears.matcher")} --DOC_HIDE
 
 assert(o.is_everything) --DOC_HIDE
 assert(o.name == "baz") --DOC_HIDE
+local rm1 = --DOC_HIDE
 matcher:remove_matching_source("first") --DOC_HIDE
+assert(rm1) --DOC_HIDE
+
+matcher:append_rules("second", {{},{},{}}) --DOC_HIDE
+
+local rm2 = --DOC_HIDE
 matcher:remove_matching_source("second") --DOC_HIDE
+assert(rm2) --DOC_HIDE