Add custom panic handler

Sadly, it doesn't seem to be called on segfaults, which means that will
still output garbage. I could install a custom segfault handler, but not
sure that's worth the effort.

src/main.zig

@@ -61,6 +61,14 @@ pub const allocator = std.mem.Allocator{
 };
 
 
+// Custom panic impl to reset the terminal before spewing out an error message.
+pub fn panic(msg: []const u8, error_return_trace: ?*std.builtin.StackTrace, ret_addr: ?usize) noreturn {
+    @setCold(true);
+    ui.deinit();
+    std.debug.panicImpl(error_return_trace, ret_addr orelse @returnAddress(), msg);
+}
+
+
 pub const config = struct {
     pub const SortCol = enum { name, blocks, size, items, mtime };
     pub const SortOrder = enum { asc, desc };