to follow the numbering of python-course project

add 2nd implementation with very tiny comparison between
the 2 implementations

adapt solutions to use functions as they are view earlier
externalize code to be dowloadable for student

it will be easier to maintain and test
it will be easier for student to recover good code

add pseudocode in solutions

we obtain a UnboundLocalVariableError

the range is not len(s) -3 but -2 as range exclude the end value