v0.2: output: explicit flushing out stdout

this is almost a must. although this may degrade performance, it means
you don't have to get 1000 messages before you get a printout of the
first one.

before this would print nothing:

 ➤ nanoline pair --connect ipc:///tmp/foo.nn | cat &
 ➤ nanoline pair --bind ipc:///tmp/foo.nn
hello

after patch, "hello" is seen echoed through `cat`.

v0.1

doc: adds readme