Board Element - add conveyor belts

[rorygraves]

Add a conveyor belt board element to the board.

Conveyor belts move the bots during the board elements phase (after all bots have performed their action).
The move the bot in the direction of the conveyor (bot direction unchanged - i.e. a bot could be move sidewise)
Conveyors may be

• single speed straight - move the bot one space
• double speed straight - move the bot two spaces
• turn (left or right) - move the bot forward, if the bot was pushed onto this by another conveyor rotate them 90 degrees in that direction).

See a better description here: chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.fgbradleys.com/rules/rules4/Robo%20Rally%20-%20rules.pdf (page 7)

• Consider joining conveyors (one feed from side, one from behind - only rotate the side conveyor.