move input stuff to src/input

src/input.zig

@@ -0,0 +1,8 @@
+const std = @import("std");
+
+pub usingnamespace @import("input/key.zig");
+pub const Binding = @import("input/Binding.zig");
+
+test {
+    std.testing.refAllDecls(@This());
+}