Provides an immutable map that can be shared between Rust, C, and languages
that bind to C in any combination. Python (using cffi) and Ruby (using
ffi) bindings are included.
Both the keys and values are returned as pointers to C strings, in memory managed by the map. Callers do not need to free said pointers.
The Ruby (bindings/stringmap.rb) and Python (bindings/stringmap.py)
provide examples of usage. In the Python case, the map has been made to
conform to the standard mapping interface.