Support for highlight and snippet function

[kaykay-dv]

sqlite3 supports highlightening search results:

SELECT highlight(email, 2, '<b>', '</b>') FROM email WHERE email MATCH 'fts5'

It would be good to have this available in the API as well, e.g. through this syntax

pocket_search.search(text="hello").values(Highlight("text",2,"<b>","</b>"))

or (which is probably more readable)

pocket_search.search(text="hello").highlight("text",2,"<b>","</b>")

[kaykay-dv]

Implemented in 0.8