SQLite gains support for window functions in 3.25.0

[DavisVaughan]

According to the developers, it mimics PostgresSQL.

https://www.sqlite.org/draft/windowfunctions.html
https://www.sqlite.org/draft/releaselog/3_25_0.html

Would also need to update the vignette section, "Creating your own database", as it mentions the current lack of window function support.
https://cran.r-project.org/web/packages/dbplyr/vignettes/dbplyr.html

[RMHogervorst]

depends on r-dbi/RSQLite#273

[krlmlr]

RSQLite PR now merged (issue in r-dbi/RSQLite#268), release planned end of February.