-preview switches

[David Gileadi]

On 4/1/20 7:15 AM, Steven Schveighoffer wrote:
> One I can see right now that is probably not controversial is the 
> markdown one.

That switch is already enabled when building DMD and Phobos 
docs--enabling it required escaping a few places where existing docs 
accidentally had markdown syntax. However I didn't enable it for 
druntime docs because they won't build on my Mac*, so I can't easily 
compare output with the switch on and off.

* src/core/stdcpp/typeinfo.d(147): Error: static assert:  "Missing 
std::type_info binding for this platform"