Change the pickup sensor to be a small rectangle in front of the robot

* Makes things much harder
Increase pickup sensor size
Added ReadingToBoolean; commented out float literals.
Added commenting to SensorVariable; added some whitespace as well.
Make KheperaIIPhenotype configurable dynamically (WIP)
Refactored float handling; the Float class is hereby banned. It is replaced by GPFloat and its subclass GPFloatLiteral; this makes it possible to ban two float literals in a GT function -- this used to be a big problem.
Added debugging aid for GT having literal children
Refactored float handling to have an explicit GPFloatVariable class
Merge branch 'master' into GP
Add a sensor for the bottom of the Khepera robot

* Used to detect target area
* Make other Khepera sensors ignore target area
* Make ChasingPhenotype a type of Khepera phenotype for testing
* Clamp the sensor output from proximity sensors to 1.0
* Fix bugs and clear up usage of PolygonSensedObject
* Make Khepera sensors more configurable
* Default Khepera sensor config to have all sensors switched off
Fixed bug with WheelDriveFromBearing claiming to have arity 2
Made epochx handle unconstructable subtrees (specifically because, GPFloatLiteral has no terminals now, so it cannot have subtrees of depth 1). Removed RandomGPFloat.
Changed tournament size to 4
Changed sensor configuration to 4 ultrasonics and 4 infrareds.
Changed population size to 400
Use JBox2D filtered collisions

* Remove isRelevantObject() method
* New abstract methods to get filter category bits and mask bits for
  Sensor
* Should be faster now :)
area stuff
Merge branch 'master' of https://github.com/JayH5/hons-simulator
Bump version
Fixed epox not parsing new SensorVariable terminals; added new genotype to Main