`BasicCrawler.export_to` should redefine the `key` and `content_type` parameters

[janbuchar]

• the key parameter is mandatory, but the user has to browse the source code or wait for a crash to know that
  • turns out LSP tells you about that... still, the docs should probably contain mandatory parameters
• going blind, I tried passing foo.csv to key and got a file called foo.csv.json, which we may also want to handle somehow
• we probably want to replace this with export_data, analogous with TS
• add get_data while we`re at it