Refactoring signature check.
Merge branch 'zmqdev' of https://github.com/tass-belgium/picotcp into zmqdev
Added and socket types and refactored them to uint8_t
Refactored Testzmtp_tests to reduce warnings, add mock to makefile
Merge branch 'zmqdev' of https://github.com/tass-belgium/picotcp into zmqdev
Refactoring zmtp_tcp_cb
Merge branch 'zmqdev' of https://github.com/tass-belgium/picotcp into zmqdev

Conflicts:
	.gitignore
Coded zmtp_tcp_cb with all it's functions (send_greeting, check_signature, check_identity,...)
resolved merging issues