Convert to addon

This is basically a working addon version. It is tested and works for singleplayer, even if you don't start in a plane or if you switch planes.

There is a known issue with having multiple "playable" units. I think that's a minor issue and that it shouldn't be a hindrance to the addon version, but will look into it regardless. I think it might be related to #4, and I suspect it needs some more handlers/checking on the state of the player and plane. See the commit message of e4025f7 for more information.

README is updated with relevant information. I also added a LICENSE file (copy/paste from README).

I don't use an event handler to see if the player is in a plane, but the `waitUntil` has a 1 second sleep, which should make the CPU footprint minuscule.

Packaged pbo included in a6ac143 and since reverted. The pbo is just a pbo packaging of `addons\arma_ccip`.

Some polishing should still be done, stay tuned.
Doesn't the endless while loop execute this all the time when the player is inside the vehicle and the engine is on?