Merge pull request #2 from hintjens/master

Problem: using custom LGPLv3+ license
Implement zmtp_msg and zmtp_connection classes
Merge pull request #3 from hurtonm/master

Implement zmtp_msg and zmtp_connection classes
Add zmtp_dealer class
Merge pull request #4 from hurtonm/master

Add zmtp_dealer class
Added autoconf packaging

- fixed includes so all classes can use zmtp.h
- added licence to source/header files
- fixed msg_size error in zmtp_connection/s_recv_msg