Merge pull request #130 from asergeyev/master

Added examples for Punycode lib. Makes godoc look pretty.
New functionality for adding private RRs to dns lib.
Added docstrings, tests and example for PrivateRRs.

(renamed CustomRR to PrivateRR)
Lots of renamed funcs and structures. More readability.
Changed logic to typeswitch and added comments.

And also added my name to contrib list as promised before.
extra docs
Merge branch 'master' of github.com:miekg/dns
Merge pull request #131 from asergeyev/customrr

Added Private RR support
Move custom* filenames to private to be in sync with the type
PrivateRR: naming naming naming

Try to find better (=more in sync with the rest of the lib) naming. My
guess is that these are better, but YMMV.
remove private rr tests into example_test.go
Fix tests and examples.

Put all examples in the same file and cleanup the tests to use
the new names.
More naming and some docs
Small doc update
small update in the README
Lowercase error output
fix example
Rename RdataLen to just Len
Rename CopyRdata to just Copy.

Still not sure if this makes things more clear.
Rename ParseTextSlice to Parse.

Shorter.