Added a check function

This function takes a date and checks if the date is formatted as
dd/mm/yyyy and returns true or false. In addition to that it will also
print a handy help message.
Added a separator function

Function takes a date formated as dd/mm/yyyy and returns an array[3]
consisted of [day] [month] [year] as integers.
Added a distance calculator function

Function calculates and shows the distance in days between two dates.
Function will two dates as arguments. This function will get called
when flag -d is raised.
Added an adder function placeholder

Function calculates a new date from given date and arbitrary number of
days. Function gets called when -a flag is raised.
Added menu call

The program will take an argument as a flag pass it to a function
introduced in commit c0b9e17f69c8d349445ad56c7b04a5ff5ec29a24 that will
then decide what function to call.