Switch usage of std::optional to nonstd::optional for now because of an
error from the Mac builder script, I cannot reproduce the problem yet
but will try to fix it later, it may not be fixable when targeting 10.7.
The header is from:
https://github.com/martinmoene/optional-lite
.
Usage is about the same, to include:
`#include "nonstd/optional.hpp"`
Then use nonstd::optional and nonstd::nullopt instead of the std::
counterparts.
Signed-off-by: Rafael Kitover <rkitover@gmail.com>