Incorrectly assumes proxyfmu.exe in working directory

[ljamt]

Currently the working directory must be equal to location of proxyfmu.exe. Running libcosim should know where to find proxyfmu.

Works:
C:\osp\cosim\bin> .\cosim.exe run C:\path\to\config\

Fails:
C:\osp\cosim> .\bin\cosim.exe run C:\path\to\config\

[markaren]

Possible solution: https://www.boost.org/doc/libs/1_77_0/doc/html/boost/dll/program_location.html

[markaren]

 if (!proxyfmu::filesystem::exists(executable)) {
        boost::dll::fs::error_code ec;
        boost::dll::fs::path loc = boost::dll::program_location(ec);
        if (!ec.failed()) {
            executable = loc.parent_path().string() / executable;
        }
    }

Should work.