handle ipv6 addresses in inet_pton and inet_ntop

implementation tested against:
https://github.com/mnaamani/enet-emscripten/blob/master/src/inet_ntop.c
https://github.com/mnaamani/enet-emscripten/blob/master/src/inet_pton.c

inet tests pass..
test_inet
test_inet2

added two new tests..
test_inet3
test_inet4