remove Scrapy dependency

[kmike]

Selectors shouldn't import from Scrapy, otherwise splitting them to a separate library doesn't provide benefits.

[pablohoffman]

nor we should duplicate code.

(incidentally, that's how w3lib got born - we needed common code from both scrapy and scrapely).

will we need to start yet another library? :-/

[eliasdorneles]

So, we ended up duplicating some utils, only: https://github.com/scrapy/parsel/blob/master/parsel/utils.py

Does someone wants to offer an alternative or are we fine with that an I can close this issue? :)

[dangra]

We can move more code into w3lib but for now the Scrapy dependency is removed