booklog: Add An Entry to booklog.csv
In ricompute/bookr: Keeps a Log of Read Books

If there is no file booklog.csv in the current working directory, a new file is created.

1	booklog(title, author = NA, date = Sys.Date(), rating = NA, notes = NA)

`title`	A character string with the title of the book. Must be quoted.
`author`	A character string with the author of the book. Must be quoted. Defaults to NA.
`date`	The date the book was finished, in the format YYYY-MM-DD. Defaults to Sys.Date().
`rating`	A numeric rating between 1 and 10. Defaults to NA.
`notes`	A character string with any notes about the book. Defaults to NA.