imperative commands

Imperative commands allow the player to bypass the unit's AI and force an action.

Two methods exists:
Method 1 (using a default command): select the target, then hold Control while you press Backspace.
Method 2 (using a command from the menu): select the command and the target, then hold Control while you press Enter.

Here are some situations where it would be useful:
Example 1: you want your units to attack a specific enemy building or unit and ignore the rest. Select the target and press Control + Backspace.
Example 2: you want your units to retreat from a place and ignore the enemy units. Select another square and press Control + Backspace.

Special case: you want to get rid of one of your units, so you force an attack on it. Select the target and press Control + Backspace.

Comment: this system is quite different from Warcraft/Starcraft, where 3 command types exist:
- "imperative" goto command (right-click on an empty place)
- "imperative" attack command (right-click on a unit/building)
- "smart" attack command (press "A" and left-click on an empty place)
I am still a bit worried about the differences in SoundRTS. The reason why I chose a different behavior is because the "imperative" commands are less efficient in most cases (unless you micromanage very quickly), so they shouldn't be the default behavior.