Study and document a methodology for effective vocabulary imporvment

[ruslkhay]

Find articles or other literature devoted to learning new words. Chosen methodology should be added into Sphinx documentation and explicitly described

[ruslkhay]

Probabilistic model should be created (something binomial):

1. Program should be working with probabilities, that current card is learned.
2. Start from $$q=1$$ or $$q = 0.95$$
3. After each iteration change values for $$p$$ and $$q$$