Extended Exercise 2.2 for clarity

Added a second exercise to get in touch with the way sequences are stored internally in the toolkit. This should help by exercise 2.3 and beyond.
moved Kleene closure def to footnote

Tried to reduce the amount of math on the notation
Aded text to Figure 2.1 for more detail
Two minor changes for clarity

Replaced "how often" by "how many times" since Eq. 2.5 is a count, "often" fits relative frequencies best.

Replaced "best" sequence by sequence that "best" explains observable data. This could be a bit ambigous.
Gave additional hint of argmax in Ex 2.8
Merge pull request #26 from ramon-astudillo/master

Changes to Day2 until Sec 2.4.2