Hooker: corrected removal order; added clear_specific().
Screen: added missing returns for bind_gate() and Unit:bind_gate().
Bind: added bind.system flag.
FieldAnimator: added optional new_duration param to Unit:reset().
Added Intro screen and shuffled systems out of Core.

Added Timer class.

Screen.Unit:
	corrected impl notify calls;
	added screen_unit back-ref to impl;
	corrected default return value for bind_gate.

Screen:
	corrected default return value for bind_gate;
	added clear();
	current(): return nil if stack is empty;
	corrected order of notify calls to be after the operation.

Core:
	moved escape bind to MainScreen;
	made all global binds system;
	moved pause stuff into pause();
	corrected bind gate behavior;
	pass LÖVE args to MainScreen.init();
	moved Hooker and Camera init to MainScreen;
	moved out all non-core system updation (MainScreen handles Hooker
	and Camera);
	changed full gfx_debug quad into four separate gray, partially
	transparent quads to show the center of the window.

Added Screens/Intro.

Screens/Main:
	renamed Unit to Impl;
	added data.impl reference;
	added get_instance();
	took non-core bindings and systems from Core;
	push IntroScreen on key 'i' and init;
	moved static initialization into __static_init().
Screens: added STUB for new repos.
main: use Gfx instead of love.graphics.
Core: delegated focus_changed(); separated crosshair debug from gfx_debug.
Added focus & pause control to MainScreen; added Screen helpers.

Screen.Unit: added notify_became_top() and is_top().

Screen/Main: added focus & pause control.
Screen/Intro: tidy.
Screen/STUB: updated to new interface.

asset: added missing atlas.intro_seq files.