[RULE CHANGE] "NO_MOVE" is no longer a legal

Previously AIs could respond with "NO_MOVE" whenever they felt like.
Officially, now they can only respond with "NO_MOVE" when they have no mobile pieces left.
(That is, only Bombs and the Flag are left).

However the game should end by a VICTORY_ATTRITION condition as soon as either player loses its last mobile piece.
So technically, "NO_MOVE" can't ever be legally printed, because the game should have ended. If it doesn't, there is a bug.

Updated webpage, updated manual, updated README

Going to email the list later today.

Goodluck!

PS: The rule change is due to a mean initial setup, for example:

**********
**********
**********
BB**BB**BB
..++..++..
..++..++..
etc

Here, Red has placed Bombs in all three "lanes". Red is unable to move.
However, as long as Red can use "NO_MOVE", an unsuspecting Blue will lose most of its pieces on the Bombs.
(Unless Blue puts a miner up the front...) But anyway, being able to not move is silly and not allowed in the real game.