Add mangling for tables with _ prefixes
Add mangling for tables with _ prefixes

Go tooling ignores files that start with _ and . so here we replace _
with a prefixing und_ (somewhat arbitrarily) to prevent collisions.

Reasoning is that `_table` and `table` are more likely to be used at
the same time than `_table` and `und_table`.

volatiletech/sqlboiler,volatiletech/sqlboiler,nullbio/sqlboiler