For this task, I've also investigated to use boost::operators
This would only incur a negligible penalty on build times and executable sizes,
however, I don't consider the boost based solution to improve readability,
since many of these comparisons are tricky or subtly different.
Moreover, since boost::operators needs to be mixed-in, the initialisation
of Symbol objects becomes difficult, not to mention the additional base class
information visible in the debugger when inspecting Symbol or Literal objects
For that reason, I decided *against* using Boost here and coded up
all the operators in all combinations manually
...which means, from now on identical input strings
will produce the same Symbol object (embedded pointer).
TODO: does not handle null pointers passed in as c-String properly
right now we have to defeat an unfortunate static assertion in
the standard library, which is expected to go away in the future.
We use a hack to hijack the problematic definition with the preprocessor,
which requires our header to be first.
