make web scraper accessible

[matyaskopp]

Reimplement simplified scraping tool and make it available within this repository.
Make package ParCzech::Scraper, because it will be needed in multiple scripts

features

• downloading (ParCzech::Scraper::Down)
  • allow using delays between http requests
  • allow saving downloaded file (use the same path as url)
  • save metadata in tsv file if available (see change folder structure #212)
  • allow using cached data
  • change relative urls to absolute
• parsing and processing (ParCzech::Scraper::Parse)
  • preprocess function
  • make some buildin preprocess finction, that can be used (allow some text polishing, like character replacements)
  • allow parsing data at all - save raw (eg for audio files)
  • traversing data (allow adding context node)
    • string and node results
    • scalar or array context