Improved non-song filtering in search_song() and _get_item_from_search_response()

[allerter]

I added the following in this PR request:

• Added the typesetter's apostrophe (’) to the punctuation characters in _clean_str()
• Added checking for lyrics_state when setting the valid variable in search_song() If the song is an instrumental, unreleased or etc, the lyrics_state key in the result that _get_item_from_search_response() returns will reflect that. Otherwise it will have the complete value.
• Added checking validity of hits inside _get_item_from_search_response() and improved matching results

This fixes #108 and #147

On a separate note, there is a line in search_song() which declared the song_info variable:

song_info = result.copy()

Why was there a need to copy result?

[allerter]

@johnwmillr, this PR is ready to be merged.