Add a more robust representation of selectors

[philss]

Add a more robust representation of selectors

[edmz]

Just curious, in you experience, is Floki.find("a + b") harder to implement than Floki.find("a.foo")?

[philss]

@edmz I think it's harder because for the Floki.find("a + b") we need to have the concept of "parent" selector, and a "parent lookup". Today it's possible to perform a descending search using Floki.find("a b"), but this is easier because we only lookup elements inside the previous selector.

Floki.find("a.foo") would require a multiple match in the same element, making it easier than the previous example since we don't need to check the "position", or parent/child element, of the target element inside the HTML tree.

[philss]

Just to let you know: I'm working on this. It's getting shape and I should have a working version soon.

[philss]

The merge of #22 closes this issue. I will open new issues related to the selectors that are missing.