Change syntax of New API in pmem package

[jerrinsg]

The syntax of the new API is currently a bit confusing. There was a suggestion in the last group meeting to pass some special type argument as the second argument of New instead of the variable name itself.

i.e., Instead of

var head *node
pmem.Init("database")
head = (*node)(pmem.New(”hd", head))

we could have something like

var head *node
type := pmem.Type(head)
head = (*node)(pmem.New(”hd", type))

What pmem.Type returns could very well be head itself but this code snippet looks more readable.