* Fixed len computation when size just goes beyond 14 bits
* Added bouds checks around 14bits
* Len() always right including when around 14bits boudaries
* Avoid splitting into labels when not applicable
* Fixed comments
* Added comments in code
* Added new test cases
* Fixed computation of Len() for SRV and all kind of records
* Fixed Sign that was relying on non-copy for Unit tests
* Removed unused padding
* Fixed typo in PackBuffer() function
* Added comment about packBufferWithCompressionMap() for testing purposes
This offset max was not taking into account leading Len() to emit a
smaller value that could not be matched by Pack(), i.e all names can
be fully compressed or used as a target for compression.
Split length tests off in seperate file length_test.go to clean up
dns_test.og a bit.