Let NbtTagList implement List<NbtTag>.

Signed-off-by: yushijinhun <yushijinhun@gmail.com>
Let NbtTagCompound implement Iterable<NbtTag>.

Signed-off-by: yushijinhun <yushijinhun@gmail.com>
Let NbtTagList implement RandomAccess.

Signed-off-by: yushijinhun <yushijinhun@gmail.com>
Merge branch 'nbt-collection' into xml