Merge branch 'buffer-read-size'

And after this patch set default evbuffer max read via bufferevent is
16K not 4K.

Here is some numbers for the single max read in evbuffer impact:
  function client() { becat "$@" | pv > /dev/null; }
  function server() { cat /dev/zero | becat -l "$@"; }

Plain bufferevent:

- 40K
  $ server -R $((40<<10)) & client -R $((40<<10))
  700MiB/s

- 16K *default now*
  $ server & client
  1.81GiB/s

- 4K
  $ server -R $((4<<10)) & client -R $((4<<10))
  1.05GiB/s

With OpenSSL (-S):

- 40K *default now*
  $ server -S -R $((40<<10)) & client -S -R $((40<<10))
  900MiB/s

- 16K *default now*
  $ server -S & client -S
  745MiB/s

- 4K
  $ server -S -R $((4<<10)) & client -S -R $((4<<10))
  593MiB/s

So as you can see without openssl 16K is faster then 40K/4K, while for
openssl 40K is still faster then 16K (I guess that this is due to with
openssl SSL_read() more at at time, while with plain we have some
allocations splits in evbuffer and maybe due to some buffer in openssl)

* buffer-read-size:
  sample/becat: bufferevent cat, ncat/nc/telnet analog
  Adjust evbuffer max read for bufferevents
  Maximum evbuffer read configuration
  Fix leaks in error path of the bufferevent_init_common_()