This commit (obviously non-atomic) cleans LIEF's code base by:
- Using pointer semantics (`std::unique_ptr<>`)
- Using LEAF boost error in the binary stream
- Reducing the scope of the iterators (`it_section`, ...)
- Removing `Structures.hpp` from the public headers
- etc
This commit removes the public include of nlohmann/json
as it is a *detail of implementation*. Instead, the public
API exposes:
```cpp
std::string to_json(...);
```
In addition, it enables to externally provide nlohmann/json using
the cmake option ``-DLIEF_OPT_NLOHMANN_JSON_EXTERNAL=on``.
For instance, this option can be used as follows:
```bash
$ cmake -DLIEF_OPT_NLOHMANN_JSON_EXTERNAL=on \
-Dnlohmann_json_DIR=<PATH>/lib/cmake/nlohmann_json
```
Related to #605
* JSON visitor are located in the format namespace
* Visitor are *real* visitor
* Visitable class has been renamed to Object
* Due to a bug in Visual Studio 2015, we move to VS2017
Romain Thomas