Update syntax, improve inferrability, and improve performance

[timholy]

This is the beginning of migrating our own internal container constructors from Container(T, args...) to Container{T}(args...). The former is old Julia syntax, the latter has advantages that you can do C = Container{T}; C(args...) (and of course pass C as an argument).

Perhaps even more important, this works around a performance problem of ReinterpretArrays in Julia 0.7+. This should be fixed in master eventually, but for now I think this workaround is important. I use unsafe_wrap and pointers rather than calling reinterpret.

@Cody-G, I believe the collection of improvements here fixes the performance (as in, speed) portion of HolyLab/RegisterQD.jl#1.

Note that this breaks RegisterMismatch; more PRs are coming!

[timholy]

Since I have a long queue of contributions I'm just going to merge without waiting for review; I'm pretty confident people want this stuff...

[Cody-G]

This is excellent, thank you Tim!