Documentation updated to reflect removal of nn_init()

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
nn_init() removed; nn_term() repurposed

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
new semantics nn_term implemented

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
Minor bug in nn_socket fixed.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
Shutdown test slightly improved

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
Bug in nn_term fixed

nn_term can be called even if there is no socket open

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
Merge branch 'noinit'