Fixed tree walker.
Improved readability by adding spaces.
Got rid of leading space.
Removed dead code.
Abstracted dumb xml tree walker subclass into a separate function.
Chnaged cost ref to rvalue ref.
Made the post bounderies more clear.
Added check for nodes that are not actually posts.
Fixed typo.
Added xpath for post id.
Added check for empty post ids instead of epty content.
Abstracted a repeated part of xpth quiries into the first query.
Added query to get op subtree.
Abstracte parse_postif into a sperated function so it can be reused for the op subtree.
Added code to parse id from the op subtree.
Abstracted parsing post text into a separate function.
Abstracted img parsing to a separate function and reused it with parsing th original post.
Added comments.
Added code to parse thread title but the node seems to be absent from the tree.