Added lowercase RRClass and RRType tests per #108.

... need to add RRSIG covering type lowercased later.
Added lowercase RR tests where TTL is in play too.
Added lowercase test strings with RR class omitted
Committing @miekg patch from gist.

https://gist.github.com/miekg/f1b1fe6dba7d6b088eec
Added test to verify RRSIG type covered in mixed case.
Added couple failure tests for lowercase class/type
Changed test for lowercase tokens; improved code:

* for cases if $ORIGIN or $TTL are used in mixed case
* changed test name too
Fixed typo in "tokens"
Removed unnecessary toUpper.
Added tests to support mixed case Type and Class
Addressed cases when tokenUpper makes sense to be used.
Merge pull request #109 from asergeyev/master

Some tokens only worked in upper case, fixing that.