Migrate scrapy-loader-upkeep into this repo

[BurnzZ]

I'll be deprecating https://github.com/BurnzZ/scrapy-loader-upkeep and migrate all of its components into this new repo.

Let's keep track of its progress on this issue:

• code migration
• test migration
• docs
• examples

[BurnzZ]

Will wait for PR #9 to be merged before adding the docs for this.

[Gallaecio]

#9 has been merged.