Palindrome tree

[indy256]

https://codeforces.com/blog/entry/13959?locale=en
http://adilet.org/blog/palindromic-tree/
https://arxiv.org/abs/1506.04862
https://github.com/indy256/olymp-docs/blob/master/notebooks/teamnote.pdf
https://github.com/ADJA/algos/blob/master/Strings/PalindromeTree.cpp
https://github.com/zimpha/algorithmic-library/blob/master/StringUtility/eertree.cc
https://www.geeksforgeeks.org/palindromic-tree-introduction-implementation/

https://www.geeksforgeeks.org/palindromic-tree-introduction-implementation/

[killacoug9]

created a pr for this, see #216