What is the official 2-player version?
According to the 2015 rulebook:
(This is not the text found in the rulebook. Please give me feedback on whether it was understandable.)
During setup, before initial placement of players' settlements, place 1 settlement of each of the unused colors on the board, one below the middle of the top row, the other above the middle of the bottom row. These represent neutral colors. Each time a player builds a road or settlement, they also place that same thing for one of the neutral colors (if no settlement is possible for either one, build a road instead). Note that a neutral color can take the Longest Road card.
Roll the dice twice each turn. If the second result is the same as the first, reroll it until it isn't.
Each player starts with 5 tokens, and may not have more than 7 at once. (The next paragraph will explain their use.) If you place a settlement adjacent to the desert hex, gain 2 tokens. If you place a settlement adjacent to water (the edge of the board), gain 1 token. (If both circumstances apply, gain 3.) This includes initial placement. Additionally, you may discard a Knight that you have played to gain 2 chips (this affects the Largest Army card).
Once on each of your turns, you may pay 1 token if you are the player with fewer (visible) points,
or 2 tokens if you are the player with more (visible) points, to take either of the following actions:
A. Put the Robber back on the desert hex (this can be done before rolling the dice, of course).
B. Take 2 resource cards at random from your opponent's hand, and then give them 2 resources of your choice.
(If your opponent only had 1 resource card, you must still give them 2.)