The reverted part of the change may use not connected socket in HTTP/1
backend.

on_SOMETHING should be used only for I/O callback functions

- zlib removed
- build of .def files removed

Fixes GH-192

Fixes GH-194

The output format is similar to `hexdump -C`

Guaranteeing NULL-termination is very useful when name or value are
used with C functions which requires NULL-terminated string.