Fix #21 The left sidebar always shows child items

[gunhansancar]

Fix #21 The left sidebar always shows child items. With this commit it checks if the section is selected then it shows everything below that section or if a node is selected only shows its children.

Replaced slashes and captured the strings because of the forward slash differences in the urls.

[vsoch]

Taking a look!

[vsoch]

I have mixed feelings about this change because it means two clicks (and page loads) to get to a child element, but in that it reflects the parent hugo theme, I think this is the correct direction to take.

[vsoch]

Thank you @gunhansancar !

[gunhansancar]

@vsoch Thanks for your efforts as well.
Yes, I tried to replicate the behaviour in the hugo theme. I actually want to have collapse/expend arrows. But I don't know what you think about it. Also this is good enough for me.

[vsoch]

My goal in creating this was to copy the original theme as much as I could, and honor those design decisions, so if the original has arrows it would make sense to add, otherwise not. I do think this is a needed change for documentation bases that are larger, and having everything expanded would make the left sidebar way too long / hard to navigate.