Additions to LuaTransportLine

[CmdrKeen]

Would it be possible to add the following API functions to the LuaTransportLine class?

- can_remove_from_front() -> boolean - can an item be removed from the front of the transportline
- remove_from_front() -> SimpleItemStack - removes an item from the front of the transportline, returns the item removed from the belt as a return value or nil if no item could be removed.

These function calls should reduce the need to call get_contents which i'm guessing is a bit expensive.