bindings: reduce the code smell

[bassosimone]

@hellais I recommend looking into each commit on it own. Detail of changes:

• stop using the pattern where we have a class composed only of static method as this is typically something that is frowned upon by C++ programmers

• rename the specific header so that it's more obviously discoverable by someone casually reading the code

• use a more obvious pattern to guarantee that we're keeping alive the object: rather than having a self referencing pointer, use instead a dynamically allocated shared pointer passed to C code

Perhaps more refactoring can be implemented in the future, but for now this seems to me a good move forward to make the code in here more obvious.

After this is merged, I can move on with making sure we wrap all we need to wrap.

[hellais]

I took a look at the commits and it looks much better like this. I am going to proceed in merging.

[bassosimone]

Very well :-)