Added a new command dispatcher that injects different parameters dynamically.

This reduces the boilerplate code needed to parse arguments in each command, and reduces the need to maintain command documentation with @Command.

Example:

@Command(aliases = "/set", desc = "Set all the blocks inside the selection to a block")
@CommandPermissions("worldedit.region.set")
@Logging(REGION)
void setBlocks(LocalPlayer player, EditSession editSession, @Selection Region region, Pattern replaceWith) {
    // Perform command
}

src/main/java/com/sk89q/rebar/command/CommandCallable.java

@@ -0,0 +1,63 @@
+// $Id$
+/*
+ * This file is a part of WorldEdit.
+ * Copyright (c) sk89q <http://www.sk89q.com>
+ * Copyright (c) the WorldEdit team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software 
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A 
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License along with
+ * this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+package com.sk89q.rebar.command;
+
+import java.util.Collection;
+import java.util.Set;
+
+import com.sk89q.minecraft.util.commands.CommandContext;
+import com.sk89q.minecraft.util.commands.CommandException;
+
+/**
+ * A command that can be executed.
+ */
+public interface CommandCallable {
+    
+    /**
+     * Get a list of value flags used by this command.
+     * 
+     * @return a list of value flags
+     */
+    Set<Character> getValueFlags();
+
+    /**
+     * Execute the command.
+     * 
+     * @param context the user input
+     * @throws CommandException thrown on any sort of command exception
+     */
+    void call(CommandContext context) throws CommandException;
+
+    /**
+     * Get a list of suggestions.
+     * 
+     * @param context the user input
+     * @return a list of suggestions
+     * @throws CommandException
+     */
+    Collection<String> getSuggestions(CommandContext context) throws CommandException;
+    
+    /**
+     * Get an object describing this command.
+     * 
+     * @return the command description
+     */
+    Description getDescription();
+
+}