Create PSO for mixed-variable problems

[expigo]

It has been decided to try using PSO for NN hyperparameter tuning. One thing to remember is that we are going to operate on values from both, continuous and discrete spaces.

[expigo]

Done, and it seems to be working:

• simplest, sphere function

• one discrete dimension, one continuous

I've implemented two methods for velocity update, the classical one, and constricted (as proposed in Eberhart, 2001). The latter converges better:

• continuous space

For classical approach, I used: omega = c1 = c2 = 0.5