ecbuf: Added simple benchmark and comparison with a naive linked list

ecbuf performs surprisingly well, it's around 4 to 8 times faster than a
regular linked list with gcc -O3. (That claim includes a performance
enhancement that I'll commit next)

Many real-world linked lists use specialized slice allocators to avoid
the malloc()/free() overhead, I've not done benchmarks against such a
solution yet.
ecbuf: Use gcc hints to indicate that buffer resizes aren't common

This provided a ~1.2 to 2 times performance improvement in the
benchmark.