Dynamic or const SQL statements

[trevyn]

Right now, the select! and execute! macros require a string literal for any raw SQL in your queries, and they do not work with a string slice or constant. You may find this limiting.

Some ideas:

• Factor the query out into its own function, and re-use that function instead.
• The Turbosql macro needs to see a string literal, but there could be an outer macro that replaces a token of your choosing with a string literal of your choosing, before it is passed to the Turbosql macro.
• Ask for a select_unchecked! or similar macro. There are significant downsides to this approach, and there are also certainly cases where it could be useful.