Add support for nth-child pseudo-selector

[joshuataylor]

It's really nice to be able to queries like:

table.some-table > tbody > tr:nth-child(1) > td:nth-child(2)

Support for floki would be awesome :)

[philss]

Thanks for the suggestion, @joshuataylor! I'm working in a refactor that will let this more easier to implement.

[gbmoretti]

I'm very interested in that feature too.
Can you give us an update about the refactoring? So maybe someone could help you to make this out :)

Thanks!

[philss]

Hi @gbmoretti! Today I could finish the POC for this refactor. The result is in this diff.

I will try to finish this until the end of this month. Please follow the issue #71 for more details.

[gbmoretti]

Thank you! I'll take a look on that :)

[philss]

Just for the record: the refactor was made in the PR #73 and I'm implementing this feature in this new branch: add-nth-child-pseudo-class.

[philss]

@joshuataylor @gbmoretti I'm sorry for the delay. This feature is now available in the version 0.12.0.

cc @EmilieP @Ali-l @Lucasosf @andrelip @aphillipo @deini @justgage @mischov