PostgreSQL support

[eksopl]

It should be pretty easy to do this on this end. The heavy lifting involved is pretty much just writing the triggers and procedures for updating _threads, _images and _daily.

Support in fuuka should also be easy enough, given that part of the work done.

Also, Connector/J is GPL, so it forces asagi to be GPLv2 encumbered. Other dependencies are Apache and BSD, with one LGPL. But since I am considering asagi to be a fuuka derivative, due to it being a completely non-cleanroom reimplementation of fuuka's dumper side, it's already dual GPLv1/Artistic License, so not much of a loss there.

[eksopl]

Pretty much done on this end, here. Needs testing to check for correctness of generated stats table, plus real-world usage stress testing.

[eksopl]

It was broken due to schema changes, barely tested, so it needs EVEN MORE testing in order to be fully okay.