make sntp client compatible with IAR

Retry to retransmit TCP packet whrn timeout elapses and there is no

memory left for now

Removed stale printf. Enforced style.

Revert "Attempt for a fix for tass-belgium#143."

This reverts commit 20bcb20.

TCP: Do not send options, if the field is empty. Cfr: tass-belgium#143

Fix issue tass-belgium#45

Task #629 Rewrite of dhcp picoapp + added dhcp functional test

Merge branch 'master' of github.com:tass-belgium/picotcp

updated manual

Moved definitions of join/leave group to pico_ipv4.c