Example of module written in C and Scheme

[jpellegrini]

@egallesio I'm not sure where this example would fit, so I included as a subdirectory of examples. Do you think it makes sense to have this?

This is an example of a STklos module written part in C and part in Scheme.

What we illustrate with this example:

• Combining C and Scheme to build an STklos module;

• Selectively exporting symbols from the C file;

• Referencing, in the Scheme file, symbols defined in the C file;

• Writing help for procedures, not only in Scheme files, but also in C files.

• The example was built for Linux, but can be adapted for other systems.

• In order to write STklos modules in C, it is necessary to understand how typical STklos C code works. This can be found in the hacking file.

[egallesio]

Hi @jpellegrini,

I have integrated your example (great idea BTW). I have modified the Makefile to permit to compile it with the STklos configuration options and without the need to have stklos previously installed. This Makefile is of course more complicated (generated by a Makefile.in …). So I have let the one you wrote for this PR as Makefile-sample for keeping things as simple as possible.

Thanks for this PR.