Added prep_sql_file function

Added a function I use to parse full SQL files.  Takes a raw SQL file, removes "--" comments, and reduces into 1 line, so that it can be fed into the run_query() function.
also for packages it's important to use `vapply` instead because it is less prone to error / producing unexpected types / simplifying when you don't want to:

```r
vec <- vapply(lines, gsub, character(1), pattern = "--.*$", replacement = "")
```