Teach uninstall handler about uninstall options.

+ Now __fisher_plugin_uninstall_handler is aware of a third argument,
`option` that can be used to indicate the event handler or uninstall
file abot any options available in `fisher uninstall`, namely, --force.

+ In addition, the uninstaller mechanism no longer receives the name of
the plugin, as this information is usually already available to plugins
anyway.

+ Finally, a path to the parent directory where the uninstall.fish file
is located is given instead of the full path to the file. Again, the
plugin usually knows the name of the file, `uninstall.fish`.

functions/__fisher_plugin_uninstall_handler.fish

@@ -1,5 +1,8 @@
-function __fisher_plugin_uninstall_handler -a plugin file
-    if source $file $plugin $file
-        emit uninstall_$plugin $file
+function __fisher_plugin_uninstall_handler -a plugin file option
+    set -l path (dirname $file)
+
+    if source $file $path "$option"
+        emit uninstall_$plugin $path "$option"
+        functions -e uninstall_$plugin
     end
 end

test/plugin-uninstall-handler.fish

@@ -1,4 +1,5 @@
 set -l path $DIRNAME/.t-$TESTNAME-(random)
+set -l option "--foobar"
 
 function -S setup
     mkdir -p $path
@@ -15,10 +16,14 @@ function -S teardown
     functions -e emit
 end
 
-test "$TESTNAME - Evaluate uninstaller with plugin name and path as arguments"
-    (__fisher_plugin_uninstall_handler foo $path/uninstall.fish | sed -n 1p) = "source foo $path/uninstall.fish"
+test "$TESTNAME - Evaluate uninstaller with path and \$option as arguments"
+    "source $path $option" = (
+        __fisher_plugin_uninstall_handler foo $path/uninstall.fish $option | sed -n 1p
+        )
 end
 
-test "$TESTNAME - Emit uninstall_<plugin> events with path as argument"
-    (__fisher_plugin_uninstall_handler foo $path/uninstall.fish | sed -n 2p) = "emit uninstall_foo $path/uninstall.fish"
+test "$TESTNAME - Emit uninstall_<plugin> events with path and \$option as argument"
+    "emit uninstall_foo $path $option" = (
+        __fisher_plugin_uninstall_handler foo $path/uninstall.fish $option | sed -n 2p
+        )
 end