Fixed links in docs, RT#66291
Fixed whatis in pod of Memcached::libmemcached::API, RT#71172
Fixed undef warnings related to expiration, RT#69996
Fixed links in docs, RT#66291
Assorted documentation tweaks
Prep for release
Handle last_return==MEMCACHED_ERRNO but lmc_state->last_errno==0 better, RT#41299.