refactor: zigify imports and correct minor mistakes

src/event.zig

@@ -1,12 +1,5 @@
 //! Events which are defined by the library. They might be extended by user
 //! events. See `App` for more details about user defined events.
-const std = @import("std");
-const input = @import("input.zig");
-const terminal = @import("terminal.zig");
-
-const Key = input.Key;
-const Mouse = input.Mouse;
-const Point = @import("point.zig").Point;
 
 /// System events available to every `zterm.App`
 pub const SystemEvent = union(enum) {
@@ -17,6 +10,7 @@ pub const SystemEvent = union(enum) {
     quit,
     /// Error event to notify other containers about a recoverable error
     err: struct {
+        /// actual error
         err: anyerror,
         /// associated error message
         msg: []const u8,
@@ -92,3 +86,10 @@ pub fn isTaggedUnion(comptime E: type) bool {
     }
     return true;
 }
+
+const std = @import("std");
+const input = @import("input.zig");
+const terminal = @import("terminal.zig");
+const Key = input.Key;
+const Mouse = input.Mouse;
+const Point = @import("point.zig").Point;