Added exercices for Level 3 and Level 4

Added Level 2 links to README

Edited readme with description and links to Level 1 exercices

Added hidenp and ft_itoa

Added str_capitalizer and rstr_capitalizer

added add_prime-sum to Level_3

Added epur_str to Level_3 and sort_list to Level_4

edited is_power_of_2 to get pass negative numbers. Added lcm for Level_3

Added wdmatch. edited

Added wdmatch

Added swap_bits and union. Edited print_bits. A bit. he he he

Added print_bits, reverse_bits and snake_to_camel

added max

added comments to first_word, minor edits to inter and added is_power_of_2 and last_word

added ft_strspn and inter