Merge pull request #3 from ates/master

Add some specs
Update rebar URL; copyright heartbeat
tcp: fix TCP checksums

1. Include the options field and padding when converting a TCP packet from
record to binary.

2. Include the length of the TCP payload in the checksum

Thanks to Garry Hodgson for reporting the bug!
ipv4: include options field

The options field was left out of the record to binary conversion.
Thanks again to Garry Hodgson for reporting this!
Improve SCTP decoding