Adds a more helpful config failure message.

It will show the list of paths search for a config file if one could not
be found.
version bump to 0.1.6
Don't fall over if we're sorting incompatible field positions. Just
do something.
Make it a little easier to enable SQL debugging.
Support table prefixes in field names.

This allows one to unambiguously refer to a field name.
e.g., When using the `play` method, `play_id` can refer
to a field in either the `play` or `play_player` tables.
Use `play_play_id` to only refer to `play` table.
Treat the sorting interaction between Play and PlayPlayer specially.

This is a pretty bad hack, but basically, we don't want the
play_player table involved in constraining results if we're sorting
by fields that are in the `play` table. Namely, we only want
the play_player table involved if we're sorting by a field that is
in play_player but NOT in play.

That this logic is buried inside the `Sorter` class is a terrible
piece of technical debt, however, the query module is due to be
scrapped and rewritten.