get_sql_update: transforms the difference of two data frame's content into...
In awerni/df2sql: transforms data frames to SQL commands

transforms the difference of two data frame's content into SQL update commands

1	get_sql_update(new_overlap_df, old_overlap_df, key_col, tablename)

`new_overlap_df`	A `data.frame` or `tibble` specifiying new vs. old overlap of the database table after the changes
`old_overlap_df`	A `data.frame` or `tibble` with new vs. old overlap of the current database table content
`key_col`	The primary key for replacements
`tablename`	The name of the database table to update from