Remove zone.go

The needs for in memory zone data are complex and different for
almost everybody. Adding a memory efficient, fast, generic and
simple data structure to go dns is therefore off the table.
Remove tests for zone
Fix IsDomainName

Make \.. legal (as it should be) and don't allocate a new var byte c
and every loop.
Actually add the MINFO parsing
Fix parsing MINFO
Acutally use the CERT parsing

Also fix some bugs in the errors it sends back
remove println
Fix length computation for TXT
Add tests for TXT record serialization
Merge pull request #42 from yalp/FixTxtLen

Fix length computation for TXT and a testcase.
Add Copyright to the new file
parsing known records as unknown ones, does not work
Reverse the test outcome
yeah
EDNS0 codes have been allocated
Add TypeToTypeString and ClassToClassString

After some discussion with Robert Edmonds, these helper functions
seems in order. It is not what he requested (that was an RRType
and RRClass as new types), but is does make sense to add some
convience functions to save some typing. The dns package itself
also used these function (4 times). So clearly there is a need.

I'm not completely sold about the names.
Created two new types: Type and Class

Actually just go with Robert's suggestion as this seems the
cleanest way to do it. Also saves me from thinking about could
names for the new functions.
Use new stuff here too
Some tweaks
Merge branch 'master' of github.com:miekg/dns