We should design SRFI 198 so that it plugs easily into libexplain -- a C
library that turns the infamously vague Unix error messages from
strerror() into more specific syscall-dependent messages.

We should leverage libexplain's code generator to output some Scheme
tables to arrive at a pure-Scheme version of libexplain.

The latest version (1.4 at the time of writing) can be downloaded here:
<https://sourceforge.net/projects/libexplain/files/latest/download>