A sourcecode of "Semicolon;" spigot server plugin. https://www.spigotmc.org/resources/semicolon.12273/

_ Semicolon.java

package ru.meloncode.semicolon;

import org.bukkit.Bukkit;
import org.bukkit.Material;
import org.bukkit.block.CommandBlock;
import org.bukkit.command.CommandSender;
import org.bukkit.event.EventHandler;
import org.bukkit.event.EventPriority;
import org.bukkit.event.Listener;
import org.bukkit.event.block.BlockRedstoneEvent;
import org.bukkit.event.player.PlayerCommandPreprocessEvent;
import org.bukkit.event.server.ServerCommandEvent;
import org.bukkit.plugin.java.JavaPlugin;

/*
  This file is part of "Semicolon;".

    "Semicolon;" is free spigot server plugin: you can redistribute it
    and/or modify it under the terms of the GNU General Public License
    as published by the Free Software Foundation, either version 3 of
    the License, or (at your option) any later version.

    "Semicolon;" 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 PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with "Semicolon;".  If not, see <http://www.gnu.org/licenses/>.
*/

public class Semicolon extends JavaPlugin implements Listener {

    @Override
    public void onEnable() {
        Bukkit.getPluginManager().registerEvents(this, this);
    }

    @EventHandler(priority = EventPriority.HIGHEST)
    public void onPlayerCommand(PlayerCommandPreprocessEvent event) {
        if (!(event.getPlayer().isOp() && event.getPlayer().hasPermission("semicolon.use"))) {
            return;
        }
        if (event.getMessage().contains(";")) {
            event.setCancelled(true);
            processCommand(event.getPlayer(), event.getMessage());
        }
    }

    @EventHandler(priority = EventPriority.HIGHEST)
    public void onConsoleCommand(ServerCommandEvent event) {
        if (event.getCommand().contains(";")) {
            event.setCancelled(true);
            processCommand(event.getSender(), event.getCommand());
        }
    }

    @EventHandler(priority = EventPriority.HIGHEST)
    public void onCommandBlockRedstonePower(BlockRedstoneEvent event) {
        if (event.getBlock().getType() != Material.COMMAND)
            return;
        if (event.getNewCurrent() <= event.getOldCurrent())
            return;
        CommandBlock block = (CommandBlock) event.getBlock().getState();

        if (block.getCommand().contains(";")) {
            event.setNewCurrent(0);
            new CommandBlockTask(event.getBlock(), block.getCommand()).runTaskTimer(this, 0, 1);
        }

    }


    private void processCommand(CommandSender sender, String message) {

        String[] commands = cleanCommand(message).split(";");
        if (commands.length > 0) {
            for (String command : commands) {
                Bukkit.dispatchCommand(sender, cleanCommand(command));
            }
        }
    }

    static String cleanCommand(String command) {
        if (command.startsWith("/") || command.startsWith(" ")) command = command.substring(1);
        if (command.endsWith(";")) command = command.substring(0, command.length() - 1);
        return command;
    }
}

CommandBlockTask.java

package ru.meloncode.semicolon;

import org.bukkit.Material;
import org.bukkit.block.Block;
import org.bukkit.block.BlockFace;
import org.bukkit.block.CommandBlock;
import org.bukkit.scheduler.BukkitRunnable;

/*
  This file is part of "Semicolon;".

    "Semicolon;" is free spigot server plugin: you can redistribute it
    and/or modify it under the terms of the GNU General Public License
    as published by the Free Software Foundation, either version 3 of
    the License, or (at your option) any later version.

    "Semicolon;" 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 PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with "Semicolon;".  If not, see <http://www.gnu.org/licenses/>.
*/


public class CommandBlockTask extends BukkitRunnable {

    String line;
    String[] commands;
    Block block;
    Block down;
    Material dType;
    byte dData;
    int i;

    public CommandBlockTask(Block block, String line) {
        this.block = block;
        this.down = block.getRelative(BlockFace.DOWN);
        this.line = line;
        this.commands = line.split(";");
        this.i = 0;
        this.dType = down.getType();
        this.dData = down.getData();
    }


    @Override
    public void run() {
        block.setType(Material.AIR); // We need this to reset CommandBlock charge. 
        //It's kind of magic, but it works.
        down.setType(Material.AIR); // Setting block under CommandBlock to air for further activation
        block.setType(Material.COMMAND); // Setting Block type to CommandBlock back.
        if (i < commands.length) {
            setCommand(Semicolon.cleanCommand(commands[i]));
            down.setType(Material.REDSTONE_BLOCK); //Activating CommandBlock
            i++;
        } else {
            //Job done. Restoring down-block and it's data. Then cancelling task
            block.setType(Material.AIR); //Preventing recursion
            down.setType(dType);
            down.setData(dData);
            block.setType(Material.COMMAND);
            setCommand(line); //Setting initial multicommand back
            cancel();
        }
    }


    private void setCommand(String command) {
        CommandBlock commandBlock = ((CommandBlock) block.getState());
        commandBlock.setCommand(command);
        commandBlock.update(true);
    }

}

Updated to v1.2
Also added licence text