Add thread-safe messages and thread-safe queues

Add thread-safe messages and thread-safe queues

* lisp/thread.el (thread--message): New cl-defstruct.
(thread-message-value, thread-message-send)
(thread-message-cancel, thread-message-wait): New functions.
(thread--queue): New cl-defstruct.
(thread-queue-empty-p, thread-queue-full-p)
(thread-queue-length, thread-queue-remove-all)
(thread-queue-put, thread-queue-get): New
functions.