`std.mem.Allocator.createOne` is renamed to `std.mem.Allocator.create`.
The problem with the previous API is that even after copy elision,
the initalization value passed as a parameter would always be a copy.
With the new API, once copy elision is done, initialization
functions can directly initialize allocated memory in place.
Related:
* #1872
* #1873
closes#1764
This adds another boolean to the test matrix; hopefully it does not
inflate the time too much.
std.event.Loop does not work with this option yet. See #1908
* add std.event.RwLock and std.event.RwLocked
* std.debug.warn does its printing locked
* add std.Mutex, however it's currently implemented as a spinlock
* rename std.event.Group.cancelAll to std.event.Group.deinit and change
the docs and assumptions.
* add std.HashMap.clone