Implement shortest common superstring algorithms

[krzysztof-turowski]

• Sweedyk - A 2 1/2-approximation algorithm for shortest superstring - 5/2-approximation
• Kaplan, Shafrir - The greedy algorithm for shortest superstrings - 5/2-approximation
• Armen, Stein - A 2 2/3-Approximation Algorithm for the Shortest Superstring Problem - 8/3-approximation
• Breslauer, Jiang, Jiang - Rotations of Periodic Strings and Short Superstrings - 8/3-approximation
• Breslauer, Jiang, Jiang - Rotations of Periodic Strings and Short Superstrings - 109/42-approximation
• Mucha - Lyndon Words and Short Superstrings - 57/23-approximation algorithm
• Paluch - Better Approximation Algorithms for Maximum Asymmetric Traveling Salesman and Shortest Superstring - 71/30-approximation