Support use_tomap everywhere

crud.pairs has use_tomap option allowing to return tuples as key-value maps instead of arrays, since there is no way to do unflatten_rows while calling pairs.

But this feature seems useful by itself. @WeCodingNow had reported that he uses crud.pairs():totable() instead of crud.select since it is impossible to write an oneliner that returns tuples as key-value maps with crud.select. There doesn't seem to be any harm in implementing use_tomap, so let's support it.

Start by locating the crud.pairs and crud.select entry points and the existing use_tomap option handling. Trace how pairs().totable() and unflatten_rows differ, then define the supported behavior for use_tomap across the relevant APIs. Done means crud.select can return tuples as key-value maps in the intended one-liner use case without breaking existing array results.