rename ptr::memcpy, memmove, memset

[brson]

Unlike the C versions these copy a number of elements, not bytes. Seemed like a good idea at the time but confused me today when I couldn't remember. Let's rename them to be clear that they are not the same as C.

I don't have any great ideas for the names at this moment.

[jruderman]

shallow_copy and podset? (Assuming you can copy structs with @ but not with ~, and can't set either.)

[brson]

These are unsafe functions, so they can copy anything, not just POD. I also noticed that vec::raw::memcpy, etc. have this same issue, they copy elements, not bytes. Interestingly, the vec docs incorrectly claim that they copy bytes.

[brson]

As discussed on IRC, calling these anything other than memcpy and memmove makes it less clear what the distinction between the two is. The pair have very well known properties regarding overlapping memory.

So any other name should indicate that distinction. I'm wondering if it's best to keep these names after all.

[brson]

@nikomatsakis suggested "copy_memory" and "copy_overlapping_memory"

[catamorphism]

I've merged pull request #4411, which fixes this.