Calculates best palindrome for given RNA sequence, and also a set suboptimal palindromes (sorted by energy)
First the complementary matrix is built, and all helixes are detected. The they are sorted by their stability. Then starting each structure with one of most stable helixes from sorted list (each time different from others), the program upgrades them with compatible helixes until adding new helix gives no stability growth or when there are no more compatible helixes. Best N structures are written to user-defined file.