fix(autoload): Set caml-mode to autoload

[jcs090218]

Add autoload to caml-mode so it can be called without doing (require 'caml). Adjust auto-mode-alist so it can be load automatically when the extensions matches.

[nojb]

The changes look good. @Chris00 is there something that can be done to help merging this?

[bbatsov]

Looks good to me as well, although I'd probably split this into two commits. You might also adjust the README, as it currently suggests setting up the file extension mappings manually.

[Chris00]

You might also adjust the README

Yes, please.

[monnier]

Hmm... I agree with the autoload cookie, of course )(and I just merged this part), but I'm not so sure about the auto-mode-alist change because I think it'll conflict with the one in Tuareg-mode.
AFAIK the "recommended" major mode is Tuareg-mode, but installing Tuareg also installs Caml-mode, so I'd rather not inflict this conflict on all the Tuareg users.
Maybe we could use major-mode-remap-alist to resolve the conflict, but that'll only be available in Emacs-30.