Get a working version!

Main news is a global rewrite of the internal class structure. In best traditions of 0.x releases.

Changes:

• Added 19133 version support.
• Turned abstract Tag into parsing root.
• Implemented direct NBT serialization.
• Implemented PHP serialization.
• Declared NBT source provider interface. With single fread() method, yes.
• Unified NbtTag::readFrom() return values.