Add make_julia_array

v0.2.3

Support for isnull, update version

Better std::complex support

v0.2.2

Fix std::complex conversion

Fix broken target name

This fixes the target name, JlCxx::jlcxx is now JlCxx::cxxwrap_julia

Initial stand-alone C++ release

This is the first separate release of the C++ part of CxxWrap.jl