* GCC5 compat: work around inherited constructor issues
Don't use inherited constructors, forward manually instead. This
basically reverts 61f803126d3cff2195d700d11d07c6578f416b23.
I believe that GCC5 does not implement P0136, a C++17 change that made
inherited constructors actually usable and was backported as a DR all
the way to C++11.
* GCC5 compat: bypass std::pair construction issue
Co-authored-by: Martin Hořeňovský <martin.horenovsky@gmail.com>
The new reporter spec generalizes key-value options that can be
passed to the reporter, looking like this
`reporterName[::key=value]*`. A key can be either Catch2-recognized,
which currently means either `out` or `colour`, or reporter-specific
which is anything prefixed with `X`, e.g. `Xfoo`.