Fix typo on chapter 2: catagory -> category
Fix typos in Chapter 3

 * positerior -> posterior
 * ontop -> on top
 * postive -> positive
 * modelling -> modeling
 * determinsitic -> deterministic
 * assingment -> assignment
 * aboves -> above
 * re-reun -> re-run
 * opimization -> optimization
 * attemps -> attempts
 * Tt is -> It is
 * retured -> returned
 * paramter -> parameter
 * esimate -> estimate
 * algoithms -> algorithms
 * specifing -> specifying
Fix typos in Chapter 2

 * assesing -> assessing
 * Determinstic -> Deterministic
 * implicity -> implicitly
 * determinsitic -> deterministic
 * intial -> initial
 * probablistic -> probabilistic
 * amoung -> among
 * explict -> explicit
 * implicity -> implicitly
 * paramters -> parameters
 * Farhenhit -> Fahrenheit
 * ocuring -> occurring
 * probabilties -> probabilities
 * specificed -> specified
 * artifical -> artificial
Merge pull request #58 from pablooliveira/Chapter3-fixtypos

Fix typos in Chapter 3
Merge pull request #57 from pablooliveira/Chapter2-typo

Fix typos in Chapter 2
Update README.md