v0.10.0: Mouse support

- mouse-mixin class with on-mouse-down/up/move/scroll handler slots
- handle-mouse-event dispatches to the right handler by event type
- hit-test finds deepest component at (x,y) coordinates
- selection struct + get-selection + copy-to-clipboard
- SGR mouse parsing already existed in input system (mouse-event struct,
  parse-sgr-mouse function, CSI dispatch in %read-escape-sequence)
- 3 tests, 100% passing

src/components/mouse-package.lisp

@@ -0,0 +1,9 @@
+(defpackage :cl-tty.mouse
+  (:use :cl :cl-tty.input :cl-tty.box)
+  (:export
+   #:mouse-mixin
+   #:on-mouse-down #:on-mouse-up #:on-mouse-move #:on-mouse-scroll
+   #:handle-mouse-event
+   #:hit-test
+   #:selection #:get-selection #:copy-to-clipboard
+   #:make-selection #:selection-p))