##VERSIONS:
1.0.25	- add a interface to rebuild drones list in case of problem :
		  /c remote.call( "drones", "rebuild", game.player )
1.0.24	- correct a problem when losing control and walking state.
1.0.23	- surveillance-drone unable to craft again (bug corrected by in bob"s library 0.14.2)
1.0.22	- temporary return to surveillance-drone category to avoid problem with bob library.
		  report done to bob.
1.0.21	- surveillance-drone unable to craft again (bug corrected)
1.0.20	- better cleaning of antennas table.
1.0.19	- factorio 0.14 compatible (but problem with surveillance-drone that can now craft things... bug reported)
1.0.18	- introduce surface change (with new on_player_changed_surface event in Factorio 0.13.16)
		- use on_player_respawned to recover new character.
		- suppress all dup feature, source of problems with surfaces.
		- add tooltips
		- compact gui size
1.0.17	- adds an emergency character recovery, just in case...
		  type /c remote.call( "drones", "lost", game.player )
1.0.16	- adapt to new find_entities working on whole surface.
		- new utils.
1.0.15	- corrects a migration version compare mistake
1.0.14	- integrate sprites, better refresh of antenna distances.
1.0.12	- when losing control of the drone, player not switched (to avoid losing the position of the drone...). 
		- You can still switch in a lost drone to see where it is. 
		- Corrects some problems with the gui_arrow when switching characters.
		- Check antenna if electric pole created or destructed.
		- Introduce a drone_antenna_radius_draw to draw an intermediate zone when building an antenna.
1.0.11	- decrease antenna power to 150kW. Make drone inventory size configurable.
1.0.10	- minor fixes
1.0.9	- 0.13 compatible. rework of initialisation routines. Drones items not hidden anymore. Custom license.
1.0.8	- more test on drones entity validity in case of data corrupted.
1.0.7	- rare bug on config change.
1.0.6	- when deleting a drone, now check if it can recover drone contents into player's inventory.
1.0.5	- add some drone antennas to place on the map to control the drones and restrict their action range. Add a "?" button to find a drone on the map. Allow maintenance drone to mine. Adjust drone speed.
1.0.4	- test version, not released.
1.0.3	- drone speed factor configurable ; main gui button only when research complete ; disable drone weapon/armor/tool/ammo by removing them automatically ; adding maintenance drone and techno upgrade. Rename mod from CameraDrones to Drones.
1.0.2	- drones are finally same force as player to simplify a lot of things, but undestructible to spy aliens. Corrects other MP bugs.
1.0.1	- gui textfield bug corrected
1.0.0	- Initial release!