Accessing unsafe functionality through the FFI seemed like a good way
to avoid writing C code, but it made things more complicated instead
of easier, and it interacts badly with a more agressive shift away
from C (such as porting to Chez Scheme). So, add functions to the
primitive `#%unsafe` module, instead.
Although "macOS" is the correct name for Apple's current desktop OS,
we've decided to go with "Mac OS" to cover all of Apple's Unix-like
desktop OS versions. The label "Mac OS" is more readable, clear in
context (i.e., unlikely to be confused with the Mac OSes that
proceeded Mac OS X), and as likely to match Apple's future OS names
as anything.
Port `examples`, `interactions`, etc., to use the new `examples`
form of `scribble/examples`. The main intended effect is to ensure
that errors are produced by examples only as specifically
indicated.
