ex. 6.1 : test + first impl
ex. 6.1 : simpler abs
ex. 6.1 : account for Int.Minvalue (not sure why this is stressed or relevant in what we are studying)
ex. 6.2: double
ex. 6.2: double - must be strictly smaller than 1
ex. 6.2: double - FIX (everything was 0 due to integer division)
ex. 6.2: double - remove println
ex. 6.3: intDouble, doubleInt
ex. 6.3: double3
ex. 6.3: formatting
ex. 6.3: double3 fix oops
ex. 6.4: ints
ex. 6.4: tailrec ints