The C and Rust versions are now comparable, with a memory-reuse and
a memory-safe version for Rust. The memory-safe version is five times
faster than the C version; the memory-reuse version (technically safe,
but can panic under some very rare circumstances) is ten times faster.
I suspect the reasons for he speedup are strictly in the `for()` loop
in the C version for copying the string, where the Rust version probably
uses memcpy() under the covers to transfer the short string into the
destination.
Added the squozen patprep function, added unit tests to the
patprep `c` code, and ensured that the rust version works the
same way. The only remaining code slowdown is that re-allocating
the Vec 50 million times turns out to be slower than re-using the
same slice of RAM over and over and over.
Elf M. Sternberg