format of world and playerdata

[ghost]

my suggestions:

• leveldb
• sqlite3

whatever it is, it has to be portable, easy to read and modify in 3rd party programs, transferable between servers and easy to backup, and it doesn't even need to be our own file format

it is also maybe a good idea to see what other softwares are doing:

• the classicworld implementation https://github.com/umby24/ClassicWorld.Net (.cw)
• level files, seems to be hugely used MCLawl/MCForge/MCGalaxy (and tons more) (.lvl)
• fcm file format fCraft/800craft (and more) (.fcm)

i don't really want to re-invent the wheel, but it isn't practical to support all of them, so we should just settle on a single one.

[ghost]

done. levelDB it is.