rename $range to $input
Introduce InputParser class
rename member[0] and member[1] as first and last member consecutively
move firstMember and lastMember into InputParser
move signs into the class
membersRange is deleted as it is used only once
move conditions into the class
signs is no longer used
firstMember and lastMember are actually left and right border
rename member as border

- starting to move getCloseMembers into the class
introduce class Set
rename members to membersInBetween
remove global function getCloseMembers as it is already moved into Set class
introduce SetWithOneMember and EmptySet
last if is not needed
decouple lastFive and firstZero from EmptySet and SetWithOneMember
add toString for Set
introduce LowBorderIncludedSet
introduce NoBorderSet
make Set inherits from EmptySet instead