Merge pull request #1 from cmur2/master

Some improvements to fix some corner cases
Add "db" as a zone file extension
Merge pull request #2 from cdodd/master

Add "db" as a zone file extension
Highlight comments after DNS records correctly

Inspired by @cdodd's work at https://github.com/sixty4k/st2-zonefile/pull/3.

This stops "eating" a DNS record when a finishing semicolon is found which is then free to be colored by the first rule of this language.