G-quadruplex/pseudoknot comprehension

[GEC-git]

Add features with G-quadruplex and pseudoknot comprehension.
This kind of secondary structures requires extended dotbracket notation. https://www.tbi.univie.ac.at/RNA/ViennaRNA/doc/html/rna_structure_notations.html

The '([{<' & string.ascii_uppercase is already included but some doubt remain about the comparison accuracy because no test have been done on this kind of secondary structure

• Perform some try on Q-quadruplex & pseudoknots and conclude about comparison reliability. /!\ The complexity comes from the G-quadruplex structures. The tetrad can form base pair in many different way and some secondary structure notation can be similar. Here is an exemple of case with the same interacting Guanine
  GGTTGGTGTGGTTGG
  ([..[)...(]..])
  ((..)(...)(..))
• #5