add bs4 dependency

and reorder reps list alphabetically for readability
test_lyrics: add onelyrics.net source
lyrics: strip title excerpt before matching

improve the extraction of lyrics title from url title and increase the
matching threshold as a consequence.
add test to check lyrics title match in url title
fix building of lyrics file paths
fix flake8
return no lyrics when HtmlParseError occured
skip test involving bs4 if python version too low
Merge pull request #992 from KraYmer/lyrics-coverage

Improve lyrics coverage