Also, they die if the get too small.

Every Bot now has 3 additional counters:
1. Food consumed from natural sources (static food)
2. Consumed remains of Bots killed by other Bots
3. Consumed remains of Bots killed by the counting Bot itself

Temporarily, these counters are printed when a Bot object is destroyed.

This improves multithreading performance on our multi-CPU server.

suggestions

The new vector type is called Vector2D and is an appropriate typedef
from Eigen::Matrix (defined in src/types.h).