Miscellaneous additions

[Skyb0rg007]

This PR adds some additional functions to different structures.

Description

Time.tick

This is the smallest time value. It is useful to be able to know what the smallest time unit is in code, and this addition was recommended in SMLFamily/BasisLibrary#35.

Universal.tagTryProject

It is a common usage pattern to do the following:

val myTag : t Universal.tag = ...
fun myFunc (u : Universal.universal) =
  if Universal.tagIs myTag u
    then doStuff (Universal.tagProject myTag u)
    else doOtherStuff ()

Because universal is implemented using an optional, this code performs additional checks.
It also encourages a bad pattern (check + unwrap) instead of pattern matching.
Now one can write:

val myTag : t Universal.tag = ...
fun myFunc (u : Universal.universal) =
  case Universal.tagTryProject myTag u
    of SOME x => doStuff x
     | NONE => doOtherStuff ()

Unsafe.ptrEq

This definition was referenced in #327, and it makes sense to add it to the Unsafe module to bless this as a valid implementation.

How Has This Been Tested?

Time.tick and Universal.tagTryProject are trivially tested, but these are trivial additions.
Unsafe.ptrEq has not been extensively tested.

[JohnReppy]

This implementation is bogus. The size of the "tick" is set by the runtime system and may differ from OS to OS. It is also the case that maybe it should be a function that returns the smallest time quanta, instead of a Time.time value.

[Skyb0rg007]

The intention of Time.tick is not for OS-level precision, but Time.time precision. As mentioned in the BasisLibrary discussion, if one is constructing Time.time values, it is important to know at what point that time value is truncated. By providing a "smallest non-zero time" value, this can be inspected.

[Skyb0rg007]

This is a replacement for the code:

fun smallestTime () = let
      fun go n = if Time.zeroTime = Time.fromNanoseconds n then go (n * 10) else n
      in  go 1 end
val tick = Time.fromNanoseconds (smallestTime ())

This is Time.fromNanoseconds 1000 in SML/NJ, which is TIME { usec = 1 }.

[JohnReppy]

I had misremembered the discussion about tick. Before putting this in the implementation, I'd like to have a Basis Library proposal for it. I'm throwing something together right now.