Start implement b&b simulator

src/interface_implementations/ballandbeam.jl

@@ -10,8 +10,9 @@ BallAndBeam() = BallAndBeam(0.01, 0.0)
 
 struct BallAndBeamSimulator <: SimulatedProcess
     h::Float64
+    state::Vector{Float64} # pos,vel,angle,ω
 end
-BallAndBeamSimulator() = BallAndBeamSimulator(0.01)
+BallAndBeamSimulator() = BallAndBeamSimulator(0.01, zeros(4))
 
 const BallAndBeamType = Union{BallAndBeam, BallAndBeamSimulator}
 num_outputs(p::BallAndBeamType) = 2
@@ -28,7 +29,7 @@ measure(p::BallAndBeam)     = io2num(ccall((:comedi_read,comedipath), Int32,
                                         (Int32,Int32,Int32), 0,0,0))
 
 control(p::BallAndBeamSimulator, u)  = error("Not yet implemented")
-measure(p::BallAndBeamSimulator)     = error("Not yet implemented")
+measure(p::BallAndBeamSimulator)     = [p.state[1], p.state[3]]
 
 const comedipath = Pkg.dir("LabProcesses","c","comedi_bridge.so")
 const conversion = 65535/20