[WIP] SQLite support for libcod

[voron00]

The async support has been added and so far has been more or less stable, but still quite experimental for now.

Currently limited to 256 rows/fields max and 512 async tasks max (you proably won't come even close to that limit).

Also added fixes to free task/db connections on map change/restart.

How to use async:

Init your async sqlite at gametype start:

		async_sqlite_initialize(); 
	

Execute your query:

		async_sqlite_create_query(level.yourdb, "SELECT SQLITE_VERSION()", ::callbackFunc, "somearg");


callbackFunc(rows, arg)
{
    printf("%\n", rows[0][0]);
} 
	

Else is similar to sqlite_query.