Merge pull request #4 from jonasborjesson/master

Initial simple version of allowing someone to change the content of captured packets
Added Record-Route and Route headers. Not done yet though...
More complete implementation of SipURI. Added more consumeXXX method to the SipParser in order to gear up for framing Via-headers. A bunch of unit tests
added support for framing Via-headers. Added support for calculating, verifying and recalculating IP checksum
Merge pull request #5 from jonasborjesson/more-sip-headers

More SIP headers + IP checksum verification