Add a mechanism for deprecating things

[xrchz]

As @marioxcc points out there is no way to indicate that something in HOL4 is deprecated, which is part of the reason why there's a whole lot of cruft that never goes away. This issue is to design and implement a mechanism to deprecate APIs, tactics, and theorems, and to use it on something.

[xrchz]

Working on #98 might be a good target for this.

[digama0]

(I think you meant @digama0 )