Julia interoperating with HEP C++ libraries

ROOT is CERN's data analysis framework, which is widely used for HEP applications. Currently, the UnROOT package supports reading the ROOT files in Julia. However, there is no support for writing into ROOT files, meaning users have to write to the ROOT files independently. This can be a pretty tedious task involving references and pointers, which is not user-friendly. The project aims to provide a write interface to the Julia community, allowing the ROOT users to experience the performance benefits of Julia and Julia users to use ROOT for HEP & data analysis without worrying about I/O. The project goal will be achieved by providing a baseline Julia package and four feature packages allowing users to write any data structure to the ROOT file. The interface will be safe, user-friendly and have a Julia-like interface.