more testing of IO/Engine functionality and a fix for the Fortran bindings
Created by: germasch
This still covers only a small piece of Engine-related IO functionality, though it was enough to find a bug in the Fortran bindings: When returning strings of 0 length from C to Fortran, the old code would leave the Fortran string in deallocated state, which leads to a crash when checking its content. Fortunately, Fortran allows for 0-size allocated arrays/strings, so the fix is to return just that.
This PR also adds adios2_engine_name()
to the C and Fortran APIs, as the same functionality exists in the CXX11 API.