Give Command updates

Updates to the `give` and `item` commands to better emulate vanilla behavior. Consolidated `give` and `item` commands into one area to facilitate code sharing and implemented basic handling of vanilla style data tags (at least the ones that currently are supported by MCServer). Also updated Info.lua file with additional information and moved `item` command to its own permission node (`core.item`). Updated README.md file included.

These changes are building towards addressing mc-server/Core#89, but before I implemented something new I figured I should fix the old.
Wow, this is clever. Will it work for the entire syntax that vanilla expects to work? And how well does it handle errors?